I'm no expert, but sailing on a lake offshore breeze can confuse the heck out of me sometimes, especially sailing into a bay. It seems to blow in to the centre of the bay and no matter how hard you try to get in there the wind twists as you get closer to shore and pushes you back. Lots of tacks to get back. Also wind at 20' high can be a little different angle than at 10' and I wind up testing both angles to see which has best drive. It may also be that for whatever turbulent blow came offshore onto the river, the H17 cut was superior in capturing the wind. I'm sure the ratings are averages where boats have their strengths and weaknesses - maybe you just found your weak spot.