Servos should ideally be mounted so that the horn is at right angles to the servo, and not in line. This would tend to mean the servo is paralel to the datum line of the plane. If it is in line, then the forces will cause the servo to pivot about the mounting screws, giving less deflection than intended, and changes to deflection depending on air speed. You would not notice this on the ground as a rule, as there is no back force from the control surfaces.

Throttle does not matter, forces are small and do not change.