Maybe I made more than one mistake in my description (I definitely made one: the third "a" in "banana" is of course a schwa, not the vowel in "arm") -- but the "a"s I put in "Banach" are (modulo incompetence) pretty much exactly the ones you'll find by clicking the "listen" link after Banach's name at the start of his Wikipedia page. So I'm not sure what you mean about "a foreign import that actually asks for it". And I just checked the etymology of "banana", and the likely Wolof original has exactly one /ɑː/ in it, in the same place as I put one. But, see above, I misdescribed how I say "banana" so I may have caused confusion.