Kees
That kinda explains why I never had much luck with a close mouth on a 45 degree plane.

The plane with the finest mouth I possesed was the Stanley #4 with a Ray Iles iron. When I bought that iron, I had to file the mouth because the iron was too thick. With some carefull filing I managed to get a mouth, which passed a 0.2mm feeler blade, but not a 0.25mm one. In US meassurements, that's between 8 and 12 thou. For me that was a very narrow mouth.

I have been planing 4 thou shavings a lot lately. Just using that fine mouth didn't help to mitigate tearout. 4 thou shavings isn't a very thin shaving. So, as a conclusion, my mouth was way too wide. I should have moved the frog a little bit. Problem with moving the frog on a Stanley plane: that's not a very precise operation.

Anyway, all that is history now. In order to be able to use the capiron without clogging issues, I grabbed a file last weekend and enlarged the mouth considerably.

I think we can safely assume you can't use the capiron close at the edge, and a mouth narrow enough to prevent tearout, at the same time.