RE: Question on 9C's actual trim range
If you look up a channel's position in the servo position screen, increments of trim are not a percentage of total travel, but just small increments of movement. Trim moves the entire throw in one direction or the other...i.e.: it adjusts the center, and the endpoints move with it. Sub-trim is in smaller increments than trim, but they are not a fixed percentage either. They will vary a bit from system-to-system, depending upon the calibration of the stick pots.
You can't look at the amount of trim deflection and then use it to determine the exact amount of sub-trim. On one of our transmitters, about 40 points of sub-trim equals about 7 points of trim. You don't want to use sub-trim to take out trim. You measure the amount of control deflection, center the trim and sub-trim, and then adjust the control surface as closely as possible mechanically, by adjusting the control linkage. Only then do you adjust sub-trim for the few fine points to get the control surface exactly right.
If you need a bunch of trim, then you'll need TONS of sub-trim to center the trim. If you add a lot of sub-trim, this can have adverse effects upon the throws, and you'll find that your endpoints have moved. It's best to adjust things so that trim and sub-trim are as close to zero as possible. Adjust control linkages first, and set sub-trim once the mechanics are as close as can be done.