With a purpose built back tension release, shooting from a forgiving valley is THE way to go. You NEED to be able to draw through the valley with these releases (Which nealy EVERY indoor shooter uses)
On the other hand, when shooting a trigger release with back tension (Like my T.R.U. ball Chappy boss...with basically NO trigger travel) it is best to shoot from a solid wall. these releases do NOT require a lot of movement to activate...just a bit more tension. These rests do best with a solid back wall...." purebred" BT releases are best used with a large soft valley.