Erica, Your Eagle is a powerful bird! In the process of trying to do it I inadvertently discovered another stretch which is very chest-expanding (no doubt the yogis know all about it) - I was (wrongly, I now realise) clasping hands behind back, and raising them with arms extended...Alice, you don't need to believe in chakras for them to exist! - what I know, from experience, is that the energy is real and can be consciously used. Maybe the imagery that you describe is just a physical thing, but maybe it can work on other levels too.
But, it never ceases to surprise me that it is possible to have that "peak experience" despite sinus problems, phlegm, lousy accoustics etc etc. The nearest I can come to pinning down the essential ingredient is the energy that seems to be there when I sing, as Bat Goddess describes, "for the love of singing" - when I sing for me (and the cat!). Then the voice can suddenly become able to cut through any obstacle with ease. I suppose the problems arise when we sing for other reasons (we've promised to, or ought to etc).
J