I know this sounds crazy (or probably obvious for you), but if something does not work or work not like you expect it to it is possible that all you need is to stop thinking about magic and just... calibrate!
I had a problem with Turnigy 9x not reaching stick limits even being set programmatically at extreme values like 120%. The problem was automagically solved after I followed this calibration guide.
Push and hold the right stick horizontal (lower) trim tab to the left, and the left stick vertical (side) trim tab up...
Sounds like a crazy shi~, isn't it? But it helped me and now both sticks work perfectly in all dimensions.