And the reason it always snaps in the same direction is probably because of wing twist. If it always snaps to the right, the right wing is stalling before the left wing. Since the left wing is still producing lift and the right wing isn't, the plane rolls. And with the tail kicked down the roll is a snap roll.

In addition to reducing the elevator throw you should check for wing twist with an incidence meter. You'll probably find the right wing tip at a more positive incidence than the left wing tip. Twist the wing panel by hand in the other direction until the covering wrinkles and reshrink it top and bottom with your heat gun. Test again. Repeat until both wing tips are at the same incidence as the wing root.

Dave