When I set up a control surface on any aircraft, I start with the pushrod on the farthest out hole of the control surface horn and use whichever hole on the servo will give me the desired travel with the ATV/Endpoints at 100% or more.
You are better off with the pushrod farther out on both the servo and the horn as this will reduce the effect of any slop in the clevises.
By moving the pushrod farther out on both ends you do not loose any mechanical advantage or resolution, just the effect of any slop.