Hi David,
I was led to believe the only factor that stalls a wing is angle of attack. I think I understand what you are saying (i.e. tweaking changes the foil shape and therefore changes the stall angle of attack).
Actually, there are many factors which let the sail or parts of the sail stall. Some are linked to the local angle of attack, the draft (camber), roughness, mast shape and perturbations and to a small amount to the speed (actually Reynolds number). Others are linked to the plan form of the sail and the its aspect ratio among many others.
The good thing of all these parameters is, that you don't have to care about them as long as you know if and where your sails stalls and how to stop it. Put tell tales in your sail and at the leech. They cause very very little extra drag, so don't be thrifty. I have them at three different heights each with a sequence of four or five tell tales from about 10cm behind the luff to the leech. With this (and a minimum transparancy of the sail of course) you will easly see the effect of sheet, downhaul and outhaul tension and mastrotation and -prebend.
Avoid stalling on the leeward side of the sail at upwind courses, if possible. But you may accept some stalling at the leeward leech if you are on a reach or going downwind. Stalling on the windward side is harmless and an indicator that you can tighten the sheet (if you are not over powered of course).
Hope that answers your question.
Cheers,
Klaus
