A typical rotating barrel carb is going to be close to full power by the time it is 65% open. The remaining rotation is going to have much less effect per degree of rotation. One only needs to look at the throttle opening and understand the amount of area open. It has a built-in curve with the greatest amount of change (per degree) being near mid-travel. As you come off idle the increase in area is increasing exponentially per degree until half throttle at which point the increase per degree reduces exponentially. A servo arm also gives the most displacement (throw) at a point 90 degrees to the thrust line (mid-point).