Usually the ATV on each channel has to be set for equal throw at the surface. An example would be that your elevator ATV may have to be reduced to 75% because the master channel always seems to have more throw then the slaved channel. I would by using sub trims make the servo arms 90 degrees to the pushrods. Then adjust mechanically so that both elevator halves are in the center position. Make sure servo arms and control horns are all equal length. Next set the elevator ATV so that you have the throw you want both up and down. The percentages for up and down will not be the same if you are adjusting for equal deflection, they will always be slightly different. Now do the same for the slaved channel with the ATV until the two halves have the same travel. Don't worry too much about what the numbers are as long as you get the same travel. You can fine tune the travel and expo for both channels through elevator Dual Rate.