I agree, I have owned a couple of Mk2's. The most recent, #436 (under restoration now) the satin black treatment behind the grille and there was evidence of it on the sills (rockers) below the stainless moldings. I acquired the car from Ron Stein, last October. The car has been off the road since 1971 or 1972. There was quite a bit of original paint still on the shell (both Polar White and Satin Black) Either way, flat or satin, would have been a bitch to maintain. You couldn't wax it, and it will water spot like crazy. I only know for sure that I'm not going to put the stripes on, as IMHO they are hideous... At least with the satin black, it's marginally easier to maintain.
Jensen applied a similar treatment to Austin Healeys, as they built the bodies.... Both behind the grille and on visible vertical flanges (with a brush) to make the body color less visible. As the Alpines and Tigers were painted by Pressed Steel, the treatments should be similar... In any event, Jensen didn't paint the satin black under the sill trim on the Mk2. I use PPG black (single stage, concept) and add about 40% by volume flatting agent and apply it with a conventional gravity spray gun.