I’m very careful about making sure that the pre-bend stays relatively consistent through the whole range of rig tension. Here’s the problem. Let’s say you’re sailing with too much pre-bend. All it takes is a centimeter or two of too much pre-bend. Then, even in 5 knots of wind, the main will be too flat. Instead of the camber at the middle stripe being 13 percent, it’s now only 12 percent or less. It takes shape and power out of the whole mainsail. The middle stripe is no longer setting up correctly for the windspeed, and that in turn affects depth at the upper and lower stripes as well. Basically, the whole sectional depth of the sail gets out of whack. So, too much pre-bend, at any rig setting, and you won’t have enough power in light air; the sail will just be too flat and wash out as you add backstay and headstay may still be too saggy. Remember, at 8 knots you’re pretty much at max power. After that you’re depowering. With too much pre-bend, you’re depowering the main too much from the start, no matter what the wind velocity and the headstay is still sagging too much. The mainsail in this scenario get washed out quickly and breaks up and the boat is overpowered because of too much headstay sag making the headsail too full.