@BaoBob - you want a tracked whatever to be located as near the head as possible to more accurately detect the sim motion that the head is being subjected to. If it’s mounted near a pivot point as in a 2 dof sim, the motions will be correct but possibly out of scale with what the tracked headset is picking up from the platform so scaling may be needed if the tracked bits are too far away and possibly different scaling on the different axes.
And it used to be a Rift sensor could get mounted on the platform and that would naturally remove the platform motion. But after Touch came out, Oculus changed their routine somewhat to rely more on the inertial sensors in the headset and mounting the sensor on the frame actually added artifacts.
Valve has said they have native motion cancellation on their roadmap but have no timetable on that that anyone outside knows. We don’t know Oculus' plans for native cancellation either. It’s probably not too tough to do since everyone is adding VR hands to flight sims but the trick is modifying the headset position to compensate.
Motion with VR is amazing. It’s also now very easy to do though there can be some expense depending on how much you scrounge, buy, and build. The software is now full-featured and easy to use and not expensive. You can get the full features for $70 with wind, vibration, and full motion. In VR with the real world blocked out, you just get lost in the experience. Xsimulator.net.