Rolf, I hadn't thought about a bubble from the mast. I feel I am oversheeting the sail to get the windward low tell to fly therefore stalling the upper portion. I did have the mast rotated, rotation control angled toward shrouds. I tried adjusting the traveler out and sheeting hard and that somewhat worked but felt slower. The low tell-tale is about 50% back. It may be as simple as rotation, should the mast be rotated going to weather? When I had the upper flowing with the lower windward tell flying up the boat could out run 16s with ease in lightish air. If the low windward tell was flying back they would stay with me or pass.