Small Universe...
Nacho, I will breath in threw the nose out through the mouth when I am doing Breathing the Universal Energy, while I'm taking a walk.
I believe that the best practice for breathing when doing the Small Universe meditation is through the nose (all the time). I think that the action of connecting the tongue to the roof of your mouth and disconnecting it repeatedly would prevent you from going deeply into the emptiness.
Of course your might choose to not connect the tongue to the roof of the mouth. However, this would be less than best for the flow of qi.
Returning to Master Lin's words you do the three depth breaths at the start, then you connect the tongue and breath through your nose.
I recommend that your stay with the meditation as described by Master Lin. You might consider taking a longer period before the meditation doing deep breathing and exhaling through your mouth.
You are perfection,
Iam2 
