Hi Etoile,
My heart goes out you. You are doing great work.
No matter where a blockage is sourced, you touch it, or effect it, from any place you practice, as far as where you are focused in your practice.
Your 'intention' is to improve, release extra energy/blockages, open up... Be it active exercise, or meditation, you move things in the right direction.
In a way, saying one should focus in the middle dan tien , or heart center, if one is experiencing depression, is a self diagnosis, similar to like someone saying their arm hurts, and they focus their to remove a blockage. Although you might find more effect from trying a different focus, remember that you are more than your blockage, and your overall wellbeing benefits from a balanced practice, or the practice of qigong in general. Something may be in your face, but at the same time, you have your whole self that benefits from your practice.
During practice, you repeatedly open up. Just the merging with the universe, opens you. Relaxation, opens you. Visualizations, aid in moving energy, releasing energy. Regardless of where you focus, you can support this basic direction of opening and releasing, in your visualizations, and always hold your intention.
There can be places one comes to in one's practice, where you feel you plateau. Perhaps, you lose a sense of progress. I spoke with Master Lin once, about this once. I think this idea is one thing, good for you to take in account. I was healthy, but feeling no progress. Sometimes, if I switched to a different exercise, I would feel something, and think it was progress. He told me that I was on the edge of a bigger change. Changing my practice gave me a new feeling, but it wasn't really progress. Rather, staying the course, would 'eventually' shift things, and things would move again. I have felt this type of cycle , more than once in my self practice. Times where you feel like you are only treading water. I have learned, that these are points of great possibility, and focused work, 'will' bring about change, and shifts to higher levels of being. Bottom line, keep your practice going, regardless of how you see your progress. Shifts will come.

Another aspect of practice, is that the energy changes. One day you feel very effective, or great from your accomplishment in practice, another day you don't, and things seem difficult. I asked Master Lin once about this too. He took his hand and made a rollercoaster gesture in the air, saying that the energy changes. Your experience might change from day to day, regarding how things go for you. Again, one has to step back and realize a bigger picture of the 'fact' that you still move in the right direction.
Back to your original question about focus in the heart. Obviously, that has to couple with a specific practice, so I assume you mean doing level II, and focusing on the middle dan tien. I would follow your intuition regarding this. If you are in a practice of either, you don't make a mistake. You are not missing the boat. Remember the basic concepts that underlie one's practice. You 'are' promoting opening up. Even when one might not feel any progress, you hold this potential, you keep doing the work,,,change will come, shifts will happen.
Mindfullness is also important. All the thinking that comes up regarding self critique of results, or just negative thoughts, or unproductive thinking, or thinking too much, etc... Try to keep your mind clear in relation to this. Keep your spirit in the driver's seat, and don't go into thoughts that don't support your work, and what you want to accomplish. It is helpful to have a method of releasing or labeling thoughts. A possible method in a SFQ language, might go like this... You finish your practice, and you find yourself thinking that you are depressed, or you question the effectiveness of what you just did, or you think about how hard it is to smile, and that it is just on the surface, etc., etc., etc.,
At the point you 'see' these thoughts, and are not blindly in them, you are in a state of 'awareness'. You could say, you are in spirit(higher self), and observing your mind.
That is a good place to be. At that point, you can say something inside, like, "That thought was not good for me, I send it back to the Universe, back to the Earth." Thoughts, are energy too. Extra energy you don't need in the case of any thoughts, that don't support your self work and intention to self heal, and transform to higher levels. You could see a sun, and send the thoughts into the sun to turn into smoke. You could exhale, and send them out with your breath. However you choose to see it would work. Labelling it, simply means to call it 'thinking', and return to the present moment.
You still make the separation, and keep the mind supporting you, and your higher self is central. Basically, you try to stay in the present moment more. This mindfullness is very important, during your session, and every moment of your day. Your mind can work against what you accomplish in your session.
This is not extra work that you have to do. Mindfullness is part of the practice.
If I was in your position, and I really wanted to do the 'best' I could for myself...
- I would establish a daily routine that stick to, and practice mindfulness, or self awareness, through out my day.
-I would set up my practice on the 'best' level. Myself, I would set a minimum at 2 hrs a day , in literal practice of my qigong. I hesitate to say that, as I don't want you to 'think', that less than this is not 'good'. It is. I am talking about 'best'.
-As I am more than my blockage, I would establish a 'balanced' practice. This may take some time to compose in the best fashion for your goals. In the beginning, a balanced approach, without something intuitive telling me what to do, would maybe look like an hour of active exercise, and an hour of meditation. Best would be an hour and an hour. Other possibilities if that isn't possible, an hour, and two half hrs. or, four half hr sessions. As I write this, I am thinking to myself, how effective it would be to do active exercise for an hour, then sit to meditate for an hour, then make a few other shorter sessions during the day! You can't over do it. You get back, everything you put into it. I had a teacher once, who simply called this 'doing the work'. It became a very positive idea to me. The word work, was not cumbersome, but rather very positive, as it yielded such positive results.
-Level I active is very effective. Within that set, you can be quite creative in what you address. The moving of yin and yang, for instance, is a very effective exercise. So internalized, the way you direct your hands back to yourself, and open up that cylinder of color light. Whether you see yourself as physical body or emotional body, works in that dynamic. You are not limited to where you bring the energy, or light. You are in a state of openess, opening, relaxed, and progressively relaxing. Slow the movement way down, so it barely moves. Expand out with the slowing down. You can do this movement matched with the inhale and exhale, at a faster pace,and that is good, but slowing it way down is better, and it is easy to lapse into emptiness in an active exercise , if you slow it way down.
- Level II active are fine too. It might be harder to experience what I speak of , concerning Level I active, in sword fingers and thunderpalms. Not so, 'from my perspective', with 10,000 hands or cloud hands. Those two, have wonderful aspects to them. 10,000 hands is a 'receiving' type exercise. Like getting blessed from the whole of heaven. Very powerful. Cloud hands, again, if you slow it down, is extremely relaxing and beautiful, in movement and visualization. Again, a powerful self healing state to be in. Sword finger and thunderpalms are good exercises, but if I were not feeling well, it might feel more an effort to focus on the purpose in the exercise, which is to focus. They have the self healing benefits, but not the same hug to them, or immersion into the same level of 'graceful' space. This is 'my' opinion. I don't want to rock anyones boats. I have spent time practicing all the exercises, and see them all as good. In some of them, like 10,000 hands, it is almost like being loved, on top of the focus and movement. This wonderful sensation, is especially nice, if you don't feel well. Same for Active level I, moving of yin and yang. A great form to practice self love in. You very much, open up within your energy field, and direct the energy back to yourself in the way your palms face you and you hold your arms. I could go on and on. Level I active is a great set of qigong exercises. As you move to the next one, you can express great release in the breathing of the universe, and, renew in the joining of yin and yang. Although your focus is lower dan tien, you are not limited to how loving you can express these movements and feelings. You can practice self love and compassion, with yourself, as you do these exercises. It is, perhaps this, that is more to the point than the mechanics of where one focus's, regarding the middle or lower dan tien. You could focus in the middle, but that in itself , is limited, without self love and compassion. This also connects to your smile. You can express compassion for yourself, even in that difficult place you speak of, trying to genuinely smile. Sometimes this opens up a great feeling of sadness, that is very good.
A genuine touching of the heart, that is opening it up and releasing. I don't equate the smile to happiness, as much as self love and compassion. You can love yourself, where ever you find yourself, happy, or depressed. It is a loving act of kindness, to smile, and then turn that smile inward. It is not like trying to hold a false sense of happiness.
- Small universe is a very good meditation. It is a way to practice longevity. It takes very good care of your body. It has great value. Slowing it down too, along with the breath, moves it to a better experience of emptiness. You also are not limited in how you work within the parameters of this meditation. You 'breath' spiritual energy, and universal energy, into these energy points and centers. You do come to the heart in this orbit. You are smiling. What will you breath, into you heart? How will you express yourself within this powerful and simple gesture? Again, the level of self love and compassion , can greatly transform a simple gesture.
Self concentration is good too. It's all good! In self concentration, I would bring in the mindfulness part. Allow thoughts. It's okay to track off. You might want to bring in an aspect of being in the present moment, and centering in higher self(spirit), and simply acknowledging the thoughts as 'thinking', and sensing a self of who you really are. Realizing self within the meditation. Focusing on awareness. Practicing compassion towards self as thoughts arise.
I don't know if the mantra CD is available, that Master Lin uses. It is used in conjunction with a heart centered meditation practice. The sound itself , carries a vibration that is good to bring into your space. The meditation technique involving this CD, might have to come from visiting a retreat at some point. This is, of course, another way to accelerate your self practice.
I hope some of this helps you, and inspires you to keep doing the 'work'. You 'will' move through this if you continue.
love,
gallen