Satin, satin, satin.

Flat should NEVER be used exterior. Just because many people do, doesn't make it right.

In order for surface texture and imperfections to be seen they have to be at a level and angle that is easy to see. You kinda have to go out of your way to look at the area on the exterior you're talking about. You see it of course, but not like it's an expanse of 100% exposed wall.

Still necessary to do good prep. I've painted that area on my homes a couple times now. Make sure it's clean and knock off any mortar boogers with a 5 in 1 or something like that. Clean, bone dry and smooth as is reasonable for block.

It is hard work, but you are SO going to love how this detail *finishes* the whole look.

Thanks! I was leaning towards satin as well. Just to be clear, though, this isn't just lower foundation walls, the house has full one-story high walls that are this concrete block "brick". Half the house is this 1950's masonry, the rest (an addition plus the gables) is shingled... Excellent prep has been done, pressure washing, caulking, and priming with SW Loxon Concrete Primer.