Engineering aspects aside, Huber did hit on what I feel is the answer to your question which was how to effectively increase the roll rate of your Avistar. The Avistar, Superstar and almost every high-wing trainer roll much bettter by having a greater amount of throw when moving up instead of down. You can do this easily by moving your servo control horn back(away from the control surface) a notch and adjusting the clevis for neutral accordingly. It's easier to see than explain but once you try it you'll see what I mean. It won't take a lot of extra through to make your Avistar roll like a champ! Good luck!

Jeff Benko
Palm Beach Skyhawks