tiggerinva,

That's interesting about the trim sensitivity on that radio. The Polk has it setable seperately for each of the 4 channels (actually, maybe not throttle, haven't checked), for each model. But yeah, it does mean you can run out of trim.

It also makes sense that the trim would follow any expo or endpoint/ATV settings you have, most trims are set up as a percentage of the stick travel, not servo travel, so yes, you wind up reducing your trim's effectiveness. You could get it back by making the trim lever more sensitive on some radios though.

In general, if you find yourself reducing throw that much using ATV or whatever, you need to go adjust the linkage and come in a hole on the servo or out on the control horn. You should always try to use full travel of the servo. My rule is, anything more than +/-20% means that my linkage needs to "change holes" somewhere. The reason behind this is that you get better control resolution and therefore better precision this way. (This sometimes shows up when a plane can't be trimmed level, one click either way is too much, etc)

In theory, I agree with FHHuber as well, that you generally want to adjust your linkages so that the trimmed neutral of the servo has the pushrod and servo arm at 90 degrees, so you get equal travel in either direction. (Unless, of course, you want more throw one way than another. I sometimes set up elevators or ailerons this way.)