RE: Question about dual elevator servos - slight problem...
If you're plugged into separate RX channels, then why the unequal pushrods? You could mount the servos facing the rear for the shortest possible pushrods, put both horns pointed to the top and reverse one of the channels.
Back to your original real question...is it possible that you have positive expo on one channel and negative on the other? That would cause this type of problem. Endpoints would be the same, but displacement anywhere other than the endpoints would be different.
Richard