I have never measured bone pressed, but it would only be about one (or maybe) two tenths of an inch difference. My body fat is less than 7%. I don't work out specifically, but I do enough exercise to keep fit. My metabolism really accounts for the way I'm built.
As far as dangerous levels of body fat goes, when one gets sick one's body preserves what we have. I once got very sick ending up in hospital, and I lost about 3 or 4 kilos. If I were fatter, I would have lost more weight. When I was diagnosed and treated, the 3 or 4 kilos returned within a couple of weeks, and I was all good again. My specialist explained to me what happened.