ORIGINAL: Tall Paul
THe servo has x amount of torque available.
Moving the pushrod out from center increases the moment arm, which increases the push available to the surface.
Force times distance.
You've got it backwards.
torque = force x distance
force = torque/distance
Doubling the length of both horns will not change the servo to surface motion, but it will halve the pushrod force.
The effect of clevis slop will also be halved.
In contrast, doubling both horns will not change the servo gear slop or servo resolution. To improve these, increase the servo throw as much as possible (to +/-45 degrees or more), by making the surface/servo horn length ratio as large as possible while still maintaining adequate surface travel. In the original photo, the surface horn looks too short, and the servo horn looks too long in comparison.