The Cornerpin tracking data from mocha MAY BE appropriate or even ideal depending on the type of rotation and if there is perspective change in the area where you want your text to stick onto.
You mentioned micha’s purple grid providing a cue that the track is rock solid. The issue with using the term grid with respect to mocha is that there is a grid object in mocha and it does reflect the tracking accuracy BUT it does not specify where exactly the tracking data is/should be. For this, you use mocha’s Planar Surface.
For Corner Pin export, the four edges of the Planar Surface defines each of the points for the Corner Pin effect. For export of transform data, the center of the Planar Surface defines the Position and Anchor Point.
Let us know if these pieces of information helps you to resolve your issue.
HTH
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