I would presume that the frame would dictate what end of the 'normal bmi' range you should be on. However, if you're a large framed person you could probably carry five or ten extra pounds that the small framed person couldn't. Vice versa applies as well, a small framed person would probably look less starved at the lower end of the 'normal bmi' range than a larger framed person.
I'm a medium framed person and in all honestly, I never used the 'big boned' excuse since it was obvious I was fat.
I did use to say I'm not overweight, I'm undertall. I'm supposed to be 6'4".