Descend to What Height?!? Good post. I would only query one comment:
"The accident report from Kegworth reccomended an improved brace possition, where you tuck your legs as far back under your seat as possible."
I don't think this is true. The angle is important but I think the knees have to be bent so that your feet lie behind the knee joint, but not all the way back. If in doubt, look carefully at the picture on the demo card which displays it correctly (at least it should in UK registered airlines). Then do what it says on the card.