I've been to that screen, and on it you can't select C1 and C2 for the Ctrl 1 and Ctrl 2 fields. The closest you can get are Sys-Ctrl 1 and Sys-Ctrl 2, but I have no idea what those are, and they don't seem to function according to what I set for them either.
For some reason the sliders work in Performance and GM mode (although their range is rather small)...