Backside on saddle, hands in the drops and weight off feet. Relax. It's a bike, not an instrument of torture. That said, if you screw up bad it might be an instrument of imminent death... but no worries. Ride faster, relax and have fun. Do you descend with the 'death grip' on the bars? If so, start relaxing your hands first. You need to be relaxed and able to move your weight around on the bike smoothly. If it's a positional thing and you can't relax because reaching the bars in the drops is too difficult, move the drops to where you can reach them comfortably. Once you get the upper body sorted out then you might stop compensating by doing weird things with your feet mid descent. If your shoes were the wrong size they'd likely be hurting nearly all the time. Even if the soles were somewhat flexible, the speedplay 3 hole adapter plates are hardly flimsy items and should spread the load nicely.