So I did a retrain for the funs and I don't think armor proficiency works on DD penalties on armor.
Before:
Effect: 1,188,683
Raw Effect: 1,398,451
After:
Effect: 1,188,683
Raw Effect: 1,398,451
No Difference.
Also, how does leadership work with DD spells? On just the damage? It makes no difference on the AMF effect.