Pixhawk 6C Tiltwing Drone Tuning

I am working with a team on a project to get a tilt-wing drone to fly in a tri-copter setup. We have 4 motors on a rotating wing setup in the front and a single prop in the rear. There are two motors on either side of the front wing and they are setup with the same pwm input in pixhawk to mimic a single motor to represent the tiltrotor tricopter setup. To function as a fixed-wing after rotating the wing we need to have the center of mass far forward on the plane, however how do we account for this when in VTOL setup? We’ve had several failures due to the nose pitching down before leaving the ground.