UltraDot accessories

I have two Matchdots that I've used for about 3 yrs now and used the polorizing lenses a few times in bad sun and was going to order a extension tube, I noticed they make a rubber eye piece for them. My question is what is the purpose for them? Do they help seeing the dot on a bright day or help center the dot up. Any ideas why shooters use them, because I might get a couple while I'm ordering a new extension tube.
Stan

The 1" rubber eye pieces work great for keeping oil off the rear lens. If you have the dot mounted far enough to the rear. On the 30mm tubes the rubber eye piece doesn't do much. Might help the eye line up a little better but doesn't seem to be much help stopping the hammer (1911) from throwing oil.

Len

Paint the rubber's back edge, end on, with a silver sharpie or other to make it into a visible circle concentric with the lens.  Like the Norman thing.

Get a Doug Halls rear shade.