1. In editor place Armed offroad and playable as gunner + subordinate in group.
2. Notice 1st person FOV is too low.
3. Register a point from the screen corners ( a rock or bush for example).
4. Press iron sights key.
5. Observe the reference point will remain in the same position.
6. Now go to 3rd person.
7. spin the camera around and you will notice it's centre of rotation is high above the centre of the vehicle.
8. Centre of rotation should be (logically) around the MG.