If you have a computer transmitter you should add -50% expo. (notice this is a negative number) You can also adjust the end point of travel, make sure you adjust both left and right (up and down) the same. They are independently adjustable.

If you do not have a computer transmitter, move the servo connections in closer to the servo, and move the connections on the surfaces farther away from the surfaces. This changes the mechanical linkages, so 30% on the servo does not produce the same deflection on the surface.

Larry