Activation of the Rotator cuffs decelerators

The PT I am training with is pretty stumped. It seems no matter what I try, I don’t feel the exercises for the deceleration in the back where I should, but near my biceps. The PT said it meant the muscle was being pinched.

Whenever I try the exercise of placing my arms against the wall, it seems that my traps are active even when I try to supress them. When I do side lying or band external rotation I feel it near the bicep, even if there is no resistance. The PT has tried holding my arm in positions that should really activate the correct muscle, to no avail. I’ve tried some other exercises, with similar focus, all in vain.

Does anyone have any ideas on what I can do? I just can’t seem to get those muscles to work, and I’m wondering if anyone else has gone through something similar.