Denis,

what windrange do you define as light? I say that 0-3m/s is light and go flat in that range. You will probably experience that the telltales will more or less demand a flatter sail in that range becouse the wind separates from the sail easier. This is even with some chop. The reasoning is that even if it takes longer to accelerate with a flat mainsail, there is just no more energy to get from the wind even with a main with more draft. Does that make sense?
In more wind and chop I want more draft, becouse then I need more power and can use it to accelerate faster after busting through chop. In more wind and flat water, the sail have more draft after manouvering and while accelerating, but is flattened for more speed after a while (changing gears)

In light winds I ignore the lower telltales. It is the top telltales where the wind is strongest and possibly skewed to the surface level wind I sail in.

By your description of the telltales I would hazard to guess that you have too much draft in the sail up there. I have no experience with the sail/mast combination!

I would try more pre-bend, more downhaul and more sheet until the telltales are streaming (leech telltales acting up/indicating separation 50% of the time)

If I am wrong, I hope the gurus will let us both know.