This has been a bit of a hobby horse for me.
BMI assumes Mass increases proportional to the square of the linear dimensions.
Whereas the mathematics I learned at thirteen years of age says Volume, and therefore Mass, increases proportional to the Cube of the linear dimensions.
It has amazed me how this simple fact has escaped legions of "experts" (and obviously mathematical illiterates) who promote the BMI nonsense.
We truly sail on a ship of fools!