Servo torque will never change irregardless of the combination you utilize. The FORCE delivered will with varying arm lengths.

It's desirable to have a mechanical advantage. Meaning the control horn pivot center or distance should be greater than the servo arm pivot distance. NEVER (in a perfect world anyway) allow the control arm to be less than the servo arm pivot distance. In your example 3/4", I'd suggest a control arm pivot spacing measured from the hinge center line to the control horn pivot point of 1".

A mechanical advantage will change the FORCE realized at the control surface.

1.0" control arm and a .75" servo arm, 1.0/.75 = 1.33:1 ratio. Nets 333oz-in of FORCE on a servo delivering 250oz-in FORCE.

If the servo was rated at 188oz-in with a one inch arm and we are using a .75" arm then we can calculate the available FORCE by dividing the known FORCE of 188 by the servo arm used of .75" and arrive at a new delivered FORCE rating with this combination of 250.66ozs of FORCE at the servo arm pivot point.

As noted above available Force will change if you use other than a 1" arm. Servos are rated in ounce-inches. So one inch is the factor used to calculate the TORQUE together with the FORCE delivered by the servo. 188ozs of FORCE x one inch = 188oz-in of TORQUE.