Denis, more draft in the sails in really weak winds results in proportionally more drag, making you a lot slower. I always got the best results with flat sails in really weak winds. 1-2 m/s. When it gets to 3-4 m/s and some chop more draft is needed for best performance. Just my general experience.

For mast rotation, where is your mast spanner/rotation control arm/lever pointing? To the daggerboard or between the daggerboard and corner of rear beam?