mrose,
My two cents and I'm looking forward to Kevin's research:
Hardpan: you know (subconscious or not) that you have to hit the ball on the way down or you will hit it fat. Thus, you have some forward lean and less loft at impact. The descending blow presents the upper edge of the groove to the ball. The groove itself doesn't spin the ball the edge of the groove does.
Perched in the grass: You hit it higher on the face because you can scoop it a little. The edge of the groove doesn't dig into the ball as drastically and you likely got some moisture between the ball and face (grass guts).
It could well be that that can happen, but not every time and it's impossible to get the same FEEL from the ball teed up on grass that you get from a tight lie. What we are trying to work out is, if you don't compress the ball against the ground then why do the two lies feel so different and have such different strikes?