Hi! I'll put more effort into balancing the rig on the beach.
I got out on tuesday, but was having the same problem all day. I basically would put my feet touching the straps, but in front. The problem is that when I hook in, the sail would have plenty of pull when it was on the other side of vertical. But it seemed like the moment it would get my side of vertical it wouldn't have enough pull to keep me up and I'd have to rescue myself from falling overboard.
I had a larger sail then most other people, I was on a 9.5 at first when the next biggest was an 8.0. I later switched down to an 8.5 as other people switched to 7.0's and further down as the day progressed. It seemed to be the same problem both times.
Still had a bunch of catapults, but this seemed to only happen from stuffing the board into a wave, or deeply burying an edge.