Changing rover actuator controls

I found this text in rover_steering_control\main.cpp. I have been unable to provide a custom mixer combination that allows for the full -1…+1 range for the throttle, so I believe the below text to be a true statement and that the issue is “deeper” than just providing a custom mixer. How / where would I go to provide the full range to the throttle?

/*

  • The PX4 architecture provides a mixer outside of the controller.
  • The mixer is fed with a default vector of actuator controls, representing
  • moments applied to the vehicle frame. This vector
  • is structured as:
  • Control Group 0 (attitude):
  • 0 - roll (-1…+1)
  • 1 - pitch (-1…+1)
  • 2 - yaw (-1…+1)
  • 3 - thrust ( 0…+1)
  • 4 - flaps (-1…+1)
  • Control Group 1 (payloads / special):

  • */