Two things: from watching Arne Moe's videos, I have learned to start my draw with a high elbow, which gets my back muscles involved early, but as I draw the bow, to bring my elbow down to where it is aligned with the arrow at full draw. That seems to work well for me.
Slouching and collapsing are two different things. Slouching means you droop your head, which means you might shorten your draw length. But if you have good back tension and a crisp release, the shot might not be all that bad, maybe just a little low. Collapsing means you are losing back tension just before release, which will cause you to hit right if it only happens a little, or way right if it degenerates into a pluck. If you video yourself in slo mo, it's quite obvious when you collapse, as you sill see your string elbow edge forward just before release. The cure for this is to really get into your back muscles and make sure you continue to pull all the way through release into follow through.
Interestingly, the cure is the same for a dynamic or dead release, just that your hand goes back farther after a dynamic release.