A question for the experts out there; to help balance my plane (CG Extra) I was planning to mount the elevator servos in the rear of the fus. I have never done this but have seen it many times.

My question is; why are the servos always mounted (external) vertically and not horizontally? I was also considering mounting the servos inside the fus. with an access panel and mounting the servos in a normal orientation with the arm protruding horizontally outside thru a "slot" in the fus. (like a aileron servo mount) Is this possible? I have never seen this configuration.

Thanks.