my friend is quite the fatty and he seems to not get stoned as easily, he doesnt smoke often so his tolerance is low
If he has a hard time getting stoned then his tolerance is not low. You can still have a high tolerance even if you don't smoke much. My friend only smokes it once a month and never in the summer, she was never big into weed and she needs about almost a gram to herself to get stoned.

Anyways, weight don't really have an effect on your buzz. Not from what I see with some people anyways.