Gremsy T7 on Ardupilot 4.3 with separate pixawk for precise compass alignment

We are trying to precisely track the sun with the gimbal.
So the Pixawk is attached to the bottom of the gimbal and rotates along with the gimbal YAW.
It is mounted on the extended plastic fitting, to direct the gimbal to the True North and to move it away from interference of the BLDCs.
I understand that the magnetic declination for the true north is already accounted for on pixawk.

Struggling with the position of the gimbal, and with incremental angle change. I.E. if north is 15 deg +, to move the gimbal 15 deg.
Also, MAV_CMD_DO_GIMBAL_MANAGER_PITCHYAW gives errors, command does not go trough.