You will need to increase the limits of the camera to be able to position it behind your shoulder, for example. This is done in the "limits_6DOF" parameter of Views.lua. Personally, I have used it this way:
limits_6DOF = {x = {-0.50,0.50},y ={-0.5,0.16},z = {-0.40,0.40},roll = 90.000000},
After that, just move the cockpit camera as usual (based on the "Cockpit Camera Move" bindings).
I've also been having trouble understanding how to make this work. In the KOLA map video trailer, the pilot turns his head as he enters what appears to be a dogfight, with a camera that provides a third-person view.
I use opentrack, but head tracking affects both the movement of the pilot's head and the camera rotation itself. And even when replaying a recorded track, any change or edit to the camera position causes the recorded head movements to be lost.