I think you are right, Erato, in that some people either consciously or unconsciously "mimic" the accents which surround them, and others remain more unaffected.
I am from London, but lived for some years in Yorkshire, where everyone asked "where are you from" the moment I opened my mouth.
My children have, however, been very amused to hear me adopt a much more Yorkshire type of accent when speaking to my mother-in-law who is from Sheffield. It's not genuine Yorkshire, of course, but I sort of feel, when speaking to her, that I need to adopt something of her way of speech.