As others have said (and I found out by testing), axial lighting is for coins NOT in holders. Since my Jefferson Nickel set is raw I decided it would be my test. Here's what I've got: It appears to work well.
Could it have something to do with the lighting you're using for slabs? I have a friend who sells a lot of slabbed toners on eBay, and he uses axial lighting with excellent results. Chris