I have not had any issue with the speed bubble with the main I bought this year. I do find that outhaul and halyard tension has a huge impact on draft depth-I've been carrying a little more tension recently, to good effect. On the halyard-I take all wrinkles out of the luff in flat water/almost any breeze.
I have found that overall rig tension helps a lot to flatten the main when breeze is on or building-in the first race at the NA's, I think (judging from photos) that we had the flattest sail on the course.
