hmmm.

first of all i don't understand what you mean if you say you've clothified them and they aren't part of a dynamic group.  i probably should have been more specific.  it's not just that a part conforms, it's also that as another group it's like a whole other piece.   i haven't so far had a problem with multiple dynamic groups.  that said, i only have one piece with a figure sitting in a dynamic dress (i don't do sitting poses much).  that's my image "The Nightcap."  looking at it, i got a fold at the waist, which i'd expect, but not like yours.  it was a while ago, and not my own dynamic dress, so i'm sure i'd use different settings today. 

it's really hard for me to say what to do without doing testing myself, and right now i'm doing a few different things and not likely to have time to play with the MFD in the near future.  that said, my general advice would be to work the two cases separately: hybrid and full dynamic.  simplify as much as possible, as grichter would advise.  so do the hybrid as close to instructions here as possible (i'm guessing you already have), and then do a completely separate sim with a MFD that's just a single dynamic group.  and try different dynamic settings.  you can do a separate test a lot of different ways (from two different PZ3 files to a single file with two dresses that you can toggle for visibility).  but the main advice i'd have is to isolate what youre varying. don't make lots of different hybrids or lots of groups that all clothify separately.  first make sure you've got cloth settings that work for that position and the fabric you want to simulate.