Many rucksacks have flaps under the buckles that stop this

A further flaw that you really only notice when wearing a thin top is that the waist strap buckles can dig in to your sides

Having just used the rucksack again over the last couple of days i have reduced the star rating to two stars and have decided to give it to a local charity shop

It doesnt work and i will have to fold the seem over and sow it down on itself