Minniflyer is correct, especially if you have a shoulder or high wing model. It sounds like you just have some differential dialed into your radio if , as you say, the geometry of the hinge line (exactly over the centerline of the moving surface hinge line)and servo wheel/arm is set up at 90 degrees at neautral. I'd suggest flying it like you have it set up, that may be the best setup, especially if you are not into precise aerobatics.