Hi. I don't remember ever hearing the term "natural minor" either hehe. I've never thought about it too much, but I think improvising on a tune with a C- or C-7 etc chord symbol, like a C minor blues, I (mostly) wouldn't use Ab in the scale but A. Dorian is the modern jazz go-to minor scale, I think. Maybe all the versions of So What/Impressions I've been listening to lately have distorted my ear :-) I'd be more likely to use a scale with a B natural than one with an Ab. Well, come to think of it, one of my complaints about the institutionalization of jazz has been that everyone learns to play the same scale over a minor chord! And it's better if everyone has their own ideas...