I just thought I'd share my fix, in case it helps.
I don't think anyone would argue that wearing armor is going to compress your bust. The armor isn't going to grow breasts to fit your body shape.
However, the armor doesn't do that. The tabard does. The armor allows breasts to clip through.
Additionally, a lot of the extra bits and bobs require custom locations because the armor was made in too many pieces.
I added the tabard slot and overlay to the chest recipes, and disabled the body parts under the tabard. That made everything look correct and clean. Everything gets equipped together, and the tabard is never equipped alone.
Then I added all the bits and bobs to the recipe that should contain them ie: 'knee' armor gets added to 'leg armor' recipe.
Now, I don't need the custom UMA any more, and the armor works well enough to use in my rpg.