It is like onion rings ... yes. No dark zones or irregularities ... but no smooth transition either. This is with a LuxV LE just screwed in without any spacer or fancy mechanism. I have no idea if something like this would actually help.
Here's the close-up:
And the LuxII to compare:
While the LuxIII is somewhat smoother there is not that much of a difference between those beams, they are quite similar. Interesting.