I modified your pic. You don't want to go aft of 25%mac, or you'll have an unstable control surface. You can go slightly forward though, and as a positive effect, the surface will become slightly stable. On the other hand, you'll be starting to make the servo work a bit harder. Also, to your original question, the F-100 Super Sabre has a physical pivot point above the flying surface itself... It then had an actuator that would move the surface fwd/aft (following a slight circular arc around the pivot point.) [8D]