Personally, I'd ignore BMI completely as it takes no account of body composition.
Before I became too old, I'd played rugby for years - during my playing days I was 15 stone - which at 5.11 is a hefty old weight.
Apparently I was about three stone overweight according to the BMI.
However, at the time I had a 36" waist (so not massive), my thighs were huge and I had a deep chest. I've also always been quite broad. I did not have even the merest hint of a belly.
Since I've given up rugby, and as I've got older, the weight has dropped off and I'm now 13 stone and a 34 inch waist. I still regularly exercise, and therefore am still forunate enough not to have a belly (I have to exercise becuase I'm one of those people who only have to smell a cheeseburger to put on half a stone).
My wife says I look gaunt and she's like me to put some weight on.......but, according to the BMI I'm still about a stone overweight.
As my wife says.......where exactly do 'they' expect me to lose the weight from???