i am afraid i dont know anything about how to access the MTP file data values from the android device side.
For ratings this is the MTP field that is written to/ read from by MusicBee:
WPD_MEDIA_USER_EFFECTIVE_RATING:
WPD_MEDIA_USER_EFFECTIVE_RATING.fmtid = New Guid(785955333, 2771, 17116, 176, 208, 188, 149, 172, 57, 106, 200)
WPD_MEDIA_USER_EFFECTIVE_RATING.pid = 17
a more common field might be the track title which i would expect an android media player to be retrieving some how
WPD_MEDIA_TITLE.fmtid = New Guid(785955333, 2771, 17116, 176, 208, 188, 149, 172, 57, 106, 200)
WPD_MEDIA_TITLE.pid = 18