I'm setting up a new model with my 783 transmitter and an R-700 receiver. I noticed something that I didn't expect. I put the servo arm on the servo so when the transmitter stick is centered the arm is as near to perpendicular to the push rod as I can get. I then us the sub trim to get the arm the rest of the way to perpendicular. I adjust the clevis at the push rod end to center the control surface so the when the stick is centered. When I move the stick from one extreme to the other, the surface travel is not symmetrical. There is now more up than down.

Is this an expected effect of using the sub-trim to finish centering the servo arm?

Thanks

It would only be an effect if your travel adjustments are maximized and the servo is reaching its stop. Otherwise the differential is in the mechanical set up likely, perhaps the control horn hook up point not on the hinge line, and other factors.