My 2 cents, I try not to even think about back tension anymore. If you're alligned properly and always pulling with the draw hand (even at anchor), correct back tension will be there on its own accord. The fact that you feel your drawing arm shoulder blade tightening indicates that you are doing what I described. When I tried to "feel" tension in my bow shoulder, my bow hand had a tendacy to swing open on release - I shoot left handed so my bow hand (right hand) would swing right on release causing a lot of right misses. Maybe someone more knowledgable will chime in.