Is the hip belt sizing the same on all of the sizes? If so, is the smallest circumference the hip belt will go the 32" mentioned in reviews below?
I don't know for sure, but I'm pretty sure that the hip belts are sized along with the pack sizes. So a small would most likely get smaller than 32". Osprey is a big time pack maker and know what they're doing.
You should be good with the small for a 32".