Hi Kev & all,
Please forgive my repetitions, and allow me again to say something regarding the smile. I guess we started with dan tiens, and moved to depression and smiling, and me posting, abundantly [ :-) ], about mindfulness!!
I agree with your perception that it is the 'feeling' of smiling that is the essence of this, as opposed to the simple physical expression.
The way you envision yourself smiling is an excellent visualization. You are supporting the manifestation of that, by holding that vision. Back to language now... You do not struggle to keep that state. Look at that part , and take the negative charge out. You do positive work as you practice that focus. What you accomplish , as far as holding your focus there, is work well done, not a state of stuggling. Whether it is trying to hold a difficult physical position, or an emotional one, one can tire, or fatigue , or lose focus. That is okay, and a part of the process and experience. Struggling, is not a pleasant experience, even if you accomplish something doing it. In a clear state of no mind, there is no struggle, just the act of doing it.
I don't mean to be over critical of anyone's words, or how they express themselves, but, it is good to take a look at it, as sometimes it connects to something one could shift to a better place in their practice.