Gill, with regards to opening up the main with the kite up, I can't really explain the aerodynamic forces, however, over the weekend, we experimented with opening up the main and easing the spin off about an arm's length while bearing off downwind (once the hull was already flying and there was a good bit of apparent wind) and we found that we could bear off and go deeper for a longer time before having to head back up to generate more apparent wind.

I actually found that by easing the main at the right time helped to power up the rig and keep our hull flying downwind. Hope this helps.