The Shoulder

Make sure that the technical execution of the test is perfect and compare several times with the other side.

an asymmetry in the shouldergirdle can give the impression that a medial rotation is being carried out less thoroughly. In that case, a good point of reference is the position of the forearm in relation to the spina scapulae. When a minor inclination of the scapula is the cause of a diminished medial rotation, then, a relatively enlarged lateral rotation will make sure that the combined range of exo-endo is the same on both sides.
a painful arc can occur with medial rotation. This is not a reason to stop the passive medial rotation at the onset of the pain. If you continue pushing, the pain may disappear again and you may still be able to finish the movement completely.