I suspect we're not talking about the same thing. As far as I can ascertain Opentrack in FS9 (even with FSUIPC), cannot give you 6DOF (6-Degree of Freedoms): yaw, pitch, roll, and the axes: x, y & z. It may be that you are seeing yaw for example, which is a rotation of your view left and right, rather than what I'm talking about - the actual movement of your head left and right. This would mean, for example, that you could move your head (and body) to the left to the point that you were looking out and past your left window - actually having your head outside and looking at the side of the aircraft. Or raising your head to see over the panel of the aircraft - similar to having your seat raised - as distinct from just rotating your head upwards, say to view your overhead panels. The issue has been discussed previously, and the conclusion seems to be that 6DOF is not possible with Opentrack in FS9.
https://www.avsim.com/forums/topic/625867-opentrack/
https://forum.simflight.com/topic/51353-setting-eyepoint-for-6dof-head-tracking/
https://forum.simflight.com/topic/97062-head-tracking-not-working-in-full-6-degrees-of-freedom/
However, anything is possible, so if somehow you've got Opentrack to work with 6DOF in FS9 - there would be many who would love to know how you were able to do this.
Paul