Well, with the DX7 TX, I used the subtrim to adjust the throttle setting so one engine would idle that same as the second engine. The carb definitely moved open wider when I adjusted the subtrim.

I had the subtrim moved almost to its max to get the right idle. Here were the effects:

1) When my throttle was at idle, both engines idled at the same RPM

2) When I moved to half-throttle, the subtrimmed engine's carb would be nearly wide open, therefore almost full throttle. The non-subtrimmed throttle was where it should have been.

3) When I pushed the throttle to full, both carbs were wide open.

4) I'm pretty sure I lined up the both servo arms on the throttle so they were perpendicular to the servo (90 degrees) before I messed around with the subtrim. So they looked the same. When I opened up the nacelle after messing around with the subtrim, the subtrimmed servo arm was deflected at least 25 degrees compared to the non-subtrimmed servo.

So if I'm thinking correctly, full-subtrim would definitely show up in the control surfaces.