For extreme bodyfat measurements, it is better to talk about absolute fat weight instead of BF percentage.
For example,
- a 250lbs bber @ 3% BF would be carrying 7.5lbs of fat mass
While,
- a 160lbs bber @ 3% BF would be carrying 4.8lbs of fat mass
The former is obviously more realistic than the latter.
I believe there are some areas/organs of the body that have to contain some fat mass - 4.8lbs is just too low, whereas 7.5lbs is more or less realistic.