With the PCM Systems, you always have 1024 steps (or 2048 with the 14MZ) in your total travel. For example, from full "UP" elevator with full "UP" trim, to full "DOWN" elevator with full "DOWN" trim you have 1024 steps. This is the same whether you have the total throw at 100%, 80%, or 130%. With smaller percentages, the steps are smaller, but you still have 1024 steps.

This may sound like you get better resolution when you decrease the percentage. That's not really so. Suppose you want your elevator to have a travel of +/- 20 degrees. If your system's set up for ATV at 100%, then you adjust the position of the pushrod on the servo and control horn to get the +/- 20 degrees. Hoping for better resolution, though, you move the ATV to 75%. That also reduces servo throw. However, by the time you adjust your servo/pushrod/control surface geometry to get the +/- 20 degrees of control surface movement, the 'size' of the steps seen by the control surface is the same as before. You've reduced the servo throw in your ATV, but then had to increase control surface throw by moving out on the servo arm and in on the control horn. The geometry 'expands' the 'compression' you performed in the radio.

For almost all purposes, the only reason you'd want regular ATV at something other than 100% for normal travel is to fine-tune the endpoints of your control surfaces' travel.