VTOL Enabling vectoring only for roll in forward flight

Hello,
I am a relatively new to the ardupilot space and I have encountered a problem while trying to setup my VTOL aircraft. My setup consists of 3 motors and 3 servos intended to be used as follows :1 for pitch, and the other 2 on each wing to control Yaw while in copter mode and roll while in forward flight.


However when trying to set the 2servos to only control roll in FWBA/manual they also react to pitch commands because there is only 1 setting (Q_TILT_FIX_ANGLE) to enable vectoring for both roll and pitch :

So my question is how can I set the servos to only control roll and not pitch as I already control the pitch with the 3rd servo on the back.

Any help would be appreciated.