It doesn''t matter if you move out on the servo or in on the surface, the mechanical advantage is the same either way. What matters is the angle of rotation of the control surface vs. the angle of rotation of the servo (measured in degrees (or radians if you want)). If you change anything, and cause the servo to move the same number of degrees, but the surface to move twice as many degrees as it did, it''s going to require twice as much torque to do it, given a constant force against the surface.

(in fact, it will take more than twice the torque to move a surface twice as far, because the pressure against the surface also goes up as the deflection increases, and that varies with airspeed)