Yes, both side to side and vertically.
It's hard for me to explain here in this thread, but if you do some geometry, and trigonometry you can see how things get out of whack the further you move away from (center center).

Will it be a big problem? probably not. You can get away with it being off a fair bit in both directions and it still work Ok.

Technically if the servo had to be mounted way below (or above) the same plane as the stab, your servo arm needs to be perpendicular to an imaginary line between the servo output gear and the hinge line. In other words the servo arm would or should not be straight up and down. However for that to work out properly the control horns would have to be set at the same angle, not 90 degrees to the control surface. Not very practical given the horns available.

Believe it or not, the only way to setup pull pull "perfect" is to have the same center to center distance on both the servo arm and the control horn with the servo 90 degrees to the control surface (side to side and up and down)

Many people believe that you can use like a 3" servo arm to a 2" control horn setup, and the linkage still work out right. It will not..
It won't be off much, but do the math and you will see.[sm=wink.gif]

Regards,
Bill