You can mount the tracker anywhere on your simulator. The position does not matter. Some mount it on the seat, mine is mounted near my steering wheel.
There has to be a good line of sight to the tracking sensor: If you run a lighthouse setup, be sure the tracker is seen at anytime by both lighthouse!
If you have an Inside-Out tracking solution, be sure that the cameras always sees the controller when you move your head. Loss of tracking results in a jumping view. You also need to take care of a flawless HMD tracking. Tracking on a motion sim is mainly disturbed by monitors that are mounted to the moving rig. Remove everything in front of you (static monitors are ok). The Walls around you have to have some high-contrast like pictures, shelfs… The camera sensors generally do look for high-contrast areas. If there is only low contrast or none (like a plain wall) the tracking will not be very solid.
The mount also to be extremely sturdy! Zip ties, tape or Velcro will not be enough. Even the slightest movement will transfer to your HMD.
A 3d printed mount is a good solution. Try to not cover any tracking points.
The tracker needs to be isolated if you notice issues from vibrations. Best way to do this is to put some vibration absorbing material between your sim and the controller. Add weight to the controller mount to increase the energy needed to excite the tracker mount to vibrate.
[Sim] < - > [Damping Material] < - > [Tracker + Mount + 500gr of weight]
Check out this video from Xammux for tracker mounting:
https://youtu.be/1MqGO46xdtI?t=624