The question was how to mount a tracker with no or just minor interference to both compasses.
I checked several positions and their influence on compass reading. Above the battery seem to be a valuable position.
It should be easy to mount or unmount because of packing reasons.
The idea was to use a kind of back pack adapter, snap it onto the battery and fix a tracker using velcro.
You can switch the mavic on/off when mounted, but the battery LEDs keeps invisible.
When I decided to upload it to thingiverse, I saw pcardon had already created a similar design. Maybe we are on the same wavelength