Quadplane throttle-deflection scaling

I’m working on a tail(belly)sitter with 2 tilt motors as the only moving pieces.
Take-off and hovering is no problem but fixed-wing flight is not working great due to the tilting of the motors being very limited at high throttle values, hence no pitch/roll authority.

Is there any way I can reduce the scaling of deflection (servo output) with throttle?
The tilt rotors deflect fine at low throttle, but at medium to high throttle the deflection is very small.
Trying to fly in fbwa.