OK, I have another idea to explain the O thing.
How might an American pronounce "eau" as in eau de toilette? Or how do you think of, say, Julie Andrews pronouncing O?
Take those pronunciations, dial them back a bit, and then compare them to how the giant in Jack and the Bean Stalk would say "Fo" as in "Fe, Fi, Fo, Fum!"
That's a little bit like the difference between a Coastal O and a Minnesota O.
Believe me, I was completely unaware of this myself, until a friend in New Orleans told me that a coworker was marveling over my accent (which again, seriously, is not particularly strong!). "Did you get how she says 'Minnesoooohhhhhta?" was the comment. That's when I started to notice there was another way to pronounce that vowel.