I'm a bit suspect about BMI too.
I'm 5'10, and according to the NHS site, if I were 9 stone something to I think 12 stone 3lb, I'd be an "ideal" weight.
The 12 stone 3lb I could buy, but 9 and a bit stone!? For a 5'10lb bloke? I was once really ill, didn't really eat for 3 months, and weighed 10 stone after that episode. Friends said I looked like I'd been in a concentration camp, so how 9 stone and a bit still falls within ideal is baffling...