I made a little video on how to improve the windrange of most sails. For example the older Witchcraft sails up to 2026 but it will work even better on sails of other brands that are cut flat. This is done by giving the middle 2 or 3 battens a bit more taper by sanding the batten tips down to 1.6mm. This has given a noticable increase in windrange of both the Karma and Slayer. For sails that are cut flat or nearly flat (meaning they are flat when lying down), this could increase the wind range even more. Flat sails need more windpower to throw profile and depend on batten taper alone for their profile stability. With more batten taper, you will need less wind to throw the profile and at the top end range, the sail will have more profile stability. It will be smoother and easier to find the angle of attack. Also batten rotation becomes softer when flipping the sail. By pulling out a batten you can check how it bends to judge whether it should have more taper. Let us know in the comments if you did and how did it work out.
