Using a 3 pound weight, I found that raising my arm up straight to the side actually did pretty much all that you said it should. Pain from the very bottom of the arc, then a bit of release throughout the middle and then pain again at the top. The difference is that my pain was highest at the top when my shoulder was most contracted. Though this could also be because the weight requires more shoulder action up top (due to gravity and less stability and the like). However, since I'm not usually ever required to lift my arm out like that I find that most of my shoulder pains come from having to stabilize a heavy grocery bag (similar to walking around with a 10 pound weight with your arm preventing its swinging) or from letting my shoulders be rolled forward too long (for instance, if seated, resting both elbows on the knee area and then pressing down on the knees with my elbows to keep my head higher and my back straighter). It also tends to get quite irritated when I hold something up in a curl position. For instance, if I'm walking about with my open laptop held by one open palm on the bottom.

Reaching into my back pocket produces hardly any irritation but trying to itch my middle-back will definitely cause pain both during and after. I also do sometimes catch myself with my elbow holding the backpack straps but I've been unable to isolate whether it was that position in particular that caused the irritation afterwards or just the fact that I was wearing a backpack. In other words, no pain during, just pain after.

As a sidenote, my physical therapists have told me that my shoulders tend to roll forward a bit (naturally) and it seems to help the situation (pain-wise) when I consciously keep them pulled back with good posture. Does that indicate anything?