Nice looking mod to your Avistar.

Take your plane up, fly straight & level and slowly add in some rudder. The plane will roll in the direction of the rudder. This is due to the high wing location on the fuselage.

What you need is 3 degrees of anhedral on both sides to compensate from the wing location. I've done several planes this way and it'll let you fly knife edge and point rolls without aileron correction. Works great on Sticks.

A trick to cure the roll without cutting the wing apart is to add downward only end plates. You can make the plate from lite ply. Cut it even with the top of the airfoil, but extend 3/4"-1" below the airfoil. Hold it to the tip with a couple of servo screws.