hi friend
so according to you eccentric movements ya movements in the opposite direction are painful.
the anteroposterior translation of humeral head during normal conditions is 4-6mm.the restraints are capsule,labrum-static stabilizers
Wikipedia reference-linkrotator cuff -dynamic stabilizers-by concavity compression action
so for excess translation/locking to take place any of the structures should be affected
have you observes the scapula kinematics
strangth of scapula stabilizers
rotator cuff special tests
tests for labral injuries
SLAP lesions
history of any trauma
general laxity