Matt, thanks for the reply, since you were there ! Without knowing where the weather mark was it`s hard to tell why you had so much fullness and twist. At first I thought you might be easing the mainsheet to get the hull back down in a gust, which Wouter also presumed.
Your following statement is interesting :
"With my current set up I have the ability to trim my sail out to be board flat if needed. I usually sail relatively light, so flatter is better for me. As you can see in the pic, making it very full is also possible. For going to weather, I set my rotation to get good transition around the leward side, which is slightly under rotated relative to traditional tear drop shapped masts. I then have my crew run the down haul so that my leach breaks equally up the sail as I sheet in. This becomes my reference point before we start, and during the leg they will downhaul more or less with the puffs. This way the sheeting is minimized, because when the sheet is eased a viscious circle is started, you get big twist to depower, but the sail also becomes very much fuller, which adds power and momentarily hurts your pointing ability, so you have to counter by letting out more sail than necessary."
I agree fully here, I`m also on the light side. In our Solo (Uni) champs a few weeks back I started playing with a few settings upwind and changed the way I play the main quite a lot (we had 12-18knots most races, 18 boats):
First get settled in on the upwind leg, main & traveller centred, downhaul on minimum. If I`m overpowered, first get the downhaul on until it`s at it`s max - If I`m still overpowered, bring mast rotation back (de-rotate), then I start playing the traveller, I will almost never ease main, since as you said it puts so much fullness into the sail initially that you first poewr up before you depower and I find the boat becomes "flighty" if you`re constantly trimming the main. Playing traveller keeps the mainsail shape & profile the same.
I found that I don`t point as high as my competition, but I have a LOT more speed than some, to the extent that I don`t worry about my heading, just foot like mad for speed, and found myself at the weather mark in the top 4 in all races. I don`t know if the way I`m adjusting the main hurts my pointing or not, but it settles the boat down and I can concentrate on my speed.
If the gust drops off I`ll ease downhaul first, then mast rotator, before coming in off the wire.

Steve