On Tuesday, March 5, 2013 2:24:09 PM UTC-5, wrote:
I completely remove the adjustable seatback so my head won't hit the canopy. This results in a slightly more reclined (and very comfortable)seating position making it easier for the lap belt to ride up. The ASW 15's cockpit doesn't have anything that forces you to bend your knees or stop you from "submarining" in the event of a sudden stop.

Does your POH allow you to remove the seatback and thereby create a submarining possibility? This also shifts the CG aft.

Some POH allow the removal of the seatback to accommodate a large pilot, so you might be technically okay.

My solution to the 'riding up' problem would be to position the lapbelt below my beer belly where it would be held firmly in place. (just kidding)