FORGET ABOUT BACK TENSION
To create a good release it's essential to have continuous movement through your expansion. The core issue with advising archers to think about back tension is a fundamental one: it is least effective for those archers that struggle the most with their release. Instead of thinking of tension, think about movement. Kim Woojin, one of the all-time greatest Korean recurve men, when asked about the recurve release, said: "It's all in the movement of the shoulders".
Your body understands movement much more naturally than tension. When you do a bicep curl with a weight, do you think about contracting your biceps and relaxing your triceps? Or do you just think about moving the hand closer to the shoulder? The answer is obvious.
The reason back tension can be destructive is because it's so easy to misunderstand. Most archers lose their movement when they feel like they are using back tension. They feel as if they are squeezing the shot through the clicker, but they are normally just overly tensing the upper traps and neck. This is exactly the opposite of what we want. It leads to fatigue, inconsistency, and a sloppy release. And it makes you more injury-prone.
A great way to think about movement instead is by doing the Elbow Direction Drill in Fig 8. As you're coming into your anchor position, get a friend or coach to lightly push an arrow against the back of your elbow. Focus on pushing against this arrow through the rest of your shot, whilst maintaining a feeling of space around the shoulder joint and neck. This will encourage the correct use of your back.
I'm not saying that thinking about back tension is wrong, but it's a much more advanced skill. To continue our gym analogy, an advanced bodybuilder might benefit from focussing on specific muscles, because they fully understand the basic movements.
Also, you definitely do want to use the large muscles of the back; they are among the strongest in your body and using them is essential to correct technique. But there is a key difference between the normal muscle engagement needed to move your shoulders and shoot, and exaggerated muscle tension that harms your shot.
This is why I prefer to think in terms of using the back muscles rather than creating tension.
Only once you have good alignment, shoulder movement, and the skill to keep expanding through the shot should you start thinking about back tension. That way you can be sure you are using it properly.