I would like to know why the [ɒ] in not often sounds different (more rounded) than the [ɒ] in hot, father, or car in American English.
I know that in British English the vowel in not is an [ɔ], but I've been taught that in American English it is an [ɒ], as in hot. However, I've noticed that the majority of Americans do not pronounce the vowel in not exactly the same as the vowel in hot; most of them produce a more rounded (and sometimes shorter) sound, similar to an [ɔ], as in dog.
For example, in the phrase It's not like that the [ɒ] in not is usually pronounced quickly and more rounded, as if it were almost a British [ɔ].
Why is this so?