Actually, you're not missing anything�you are partially right. While the strap is connected to your arm it is hard to use back tension because your hand is also connected to the arm which is connected to the strap. I know some people that claim to be using back tension, but when watching them it is obvious they are using finger pressure instead�possibly a subliminal thing. However, it is possible and it is very hard for me to explain, but what I have found is that if you begin to apply pressure to the trigger and stop just before it fires and then relax your hand while pulling back with your back muscles it can go off. You will never get it to go off just by touching the trigger and pulling with your rhomboids as you correctly stated�you have to already be applying pressure with your finger...it works better with a bow that has a very solid wall.
Or............you can just by a wrist style of release that Tim Gillingham uses called the Rip Shot. It actually uses the back tension via the elbow/back muscles.
For the record....I have made my wrist strap release go off with back tension, but not with any amount of consistency at all, and it is a complete surprise when it happens�more of a surprise than the normal surprise. Shocked actually might be a better description..LOL.
