How to avoid Boarding Group D/E?
 

When booking MC, does anyone know how seats get assigned to boarding groups? I've been on some recent flights where being in boarding group D or E can determine whether or not I wind up gate-checking my bag (I have a flight tonight where I've been stuck in E, which has me nervous).

I know First Class, MCS, etc get boarded first, and I can pay $20 for MCE if I thought it worthwhile, but I'd like to be among the first MC folks to board if there's a secret to it...

If you want to be right after MCS/Elites, then you have to pony up for MCE. That automatically gets you in group A. I thought after that the farther back in the plane you sit the farther down the group ladder you are. Can someone confirm or correct that?

Back of the plane
 

After the "special" seats, they start boarding the back of the plane first. So pick a seat towards the back to avoid D and E.