Where you end up in the pile has very little to do with your boats seat position. Your seat position only keeps your boats trim level while sitting in the water (not bow or stern heavy, but just right, thus stable, relatively fast). Controlling where you are on the pile takes lot's of practice, and most tricks require setting up on the top of the pile (as you realize). Briefly, aggressively, engaging your downstream edge in a side surf will usually get you to the top of the pile (this makes you bounce). Otherwise, work the corners and weak seams in the pile.