Yeah, the proportions in im@s are a bit off, to say the least, but as animagic4u said, it body structure plays a big role in this too.
It IS odd that Kanako is considered chubby by iM@S standards, yet when taking her measurements into real life context, she'd be the world's greatest supermodel.
Kanako's measurements, when converted into inches, are 35-25-35, so that means she has a pretty good hourglass figure going on. However, her height in inches is about 5 feet, so she's more of a short and curvy gal than anything. Her art is depicts her as slightly chubby but otherwise unremarkable, which shouldn't really be the case given her measurements. Really, most of the girl's measurements would give them hourglass figures-- Yukiho's measurements, when converted to inches, are about 32-22-32, and she's 5 foot 1.
Anyways, I think the wonky proportions stem from some combination of the creators not knowing how sizing and proportions work and the fact that anime girls aren't required to have realistic bodies. I will say though, that it's a bit odd that the girls don't actually look like they have super-ridiculous proportions. I guess it's a good thing they don't look like this, haha.
