Actually, it's the other way around. By adding two additional servos to independently control the elevator, you are decreasing the amount of control surface This makes the plane less pitch sensitive. With only two servos, all four control surfaces were being used to control pitch. With four servos, only two control surfaces are being used. The plane will still be very maneuverable, but not so sensitive that it is unmanageable in flight. I hope this is correct. Opjose will correct me if I'm wrong.