Singers tend to do things without knowing exactly what is going on, and I am no exception. What I think I am doing, is pushing my diaphragm down when I inhale, and letting it push the contents of the abdomen downwards and outwards, as deep as possible in the torso. When I start singing, I tighten the pelvic and abdominal muscles in order to push the contents of the abdomen upwards against the diaphragm, but I keep pushing the diaphragm downwards as an antagonist. This double action lets me control the pressure, the speed and the flow of air - liberating the muscles around the throat from that particular task. Sometimes I expand the breast cage in order to tighten the diaphragm if I feel it needs more tension. Does this sound plausible?