Aha! I think I am about to have it "got".
I suspect that the aforesaid adapters would have some optical element built in to accommodate these lenses, thus effecting a crop of the image on the sensor.
If this is not the case, then I own to still being baffled, bamboozled (with figures optional), even balderdashed, or almost anything suitable that starts with "ba".
(But maybe not black sheep.)
m.