I think about it in an indirect way
- keep the drawing elbow high so it's at or above the level of the arrow
- bring the drawing elbow round until it feels like it's in line with the shoulders (it isn't of course, but that's how it feels)
- you should then sense the back muscles tensing on both the drawing side and the bow side.
I don't think the direct technical explanations about scapula movements are helpful to most archers.