ORIGINAL: Ram Jet
I remember reading here in a recent post that it's more important that the servo arm be 90 degrees to the push rod or cable termination than 90 degrees to the servo itself. I don't know from experience.
Bill
Having the control rod 90* to the servo horn (tangential to the arc) ensures equal travel in both directions. The benefit of having the rod 90* to the servo is to use minimize movement of the servo in the plane by having the forces act along the length of the servo instead of across the servo. I would argue that having the rod 90* to the servo horn is more important for precise control.