I don't own those units so can't really comment...what I can say is that when I made the switch to MH, I was clueless as to how they were suppose to sit. They were DE bulbs, so I lined them up with the notches and pushed down. (not very hard however)...thinking that was it. But my bulbs were loose, and wouldn't stay in the fixture. After trying to figure out why for about an hour, I realized that I was suppose to use quite a bit of force to make sure they really seated in the notches. I felt like an idiot, but that's my experience with loose DE bulbs. Maybe you are experiencing something similar.