The comptip is more flexible than the alu stick so I would guess the sail dont have enough luff curve in the upper section. Dont sound that way by your description though, sounds more like you have too much luff curve? You are certain the lower windward telltale is not acting up becouse there is a separation bubble behind the mast becouse of overotation? How far back is the lower windward telltale, 50%?

Photos of your different trims?

If your only problem is the lower windward telltale that is really good.