I’m not at all this will be of help to but it helped me in so many ways for rotation.
It is an exercise where you use your arm to make a hitchhiker sign.
I could not do it at all without help from my other hand, good shoulder side.
I would rest my arm on the dining room table and perform this exercise with the help of my hand to push the arm to through out a hitchhiker thumb sign.
I now am able to several motions I couldn’t do before.
My PT. never had me perform this exercise or told me about it. I came across it on the internet when searching for answers to my limited rotations for shoulder/ arm.
Try it.
By the way I had a RTSA surgery. Several tears in my rotator cuff and extreme osteoarthritis.