SPACE TRACKER
Optional Space Tracker
A optional feature when using Vive trackers with the Oculus branch is to use a HMD Tracker also referred to as a "Space Tracker".
A space tracker can be attached directly to the Quest HMD and helps to keep both playspaces aligned at all times.
From Mocap Fusion locate the Settings menu, under Devices locate the SPACE TRACKER dropdown and select your HMD type, This step is important!!
Using rubber bands attach the Space Tracker to the HMD. The alignment must be the same as shown in the videos. Be certain that the USB charging port is facing in the proper orientation.

Quest 2 - HMD Tracker
Space tracker alignment instructions for attaching a Vive tracker 3.0 to the Quest 2 HMD.

Quest Pro - HMD Tracker
Space tracker alignment instructions for attaching a Vive tracker 3.0 to the Quest Por HMD.
Space Tracker Setup
Assign the optional space tracker from the Trackers Setup menu. Locate the tracker attached to the HMD and set it as "Space".
Afterwards you should notice all of the tracker are now aligned with the avatar.
By tilting or rotating the HMD you should see the green motion bar changing, set this tracker as "Space" tracker.