In the interest of fairness, it should be said that there are basically 2 types of caps:
1) The type where there is supposed to be a significant gap between the top & bottom halves
2) there shouldn't be a gap or the gap is so small that its almost not there.
In the case of #2, lapping might ruin the rings, especially if they are significantly out of alignment.....so what are you to do if they are out of alignment? Exchange for some replacements or find different ones, check that your rail is straight & square.
For example I have some Arken rings that did not give me any indication that they should be lapped so I didn't. The gaps on the bushnell scope are so small that I can't fit a fingernail in them. Very much lapping and the caps will touch before clamping on the tube. Now it could be the scope being on the smaller side or the bores on the larger side, I'm not sure. But the rings were aligned, the scope sat in the bottoms so well, and installation marks have been so minimal that I dont feel the need to lap them.