We have 3 bits, child, bike and seat. Its an older-style Hamax rear seat with a clamp for attaching to the down tube. Child is still under the weight (28kgs - seat is Max 40kgs) but the clearance is not great - there's about 1", but when the surface is a bit bump its catching the wheel. There would be room on the down tube to raise it by 3 inches or so but there is a guide-boss for the gear cable which prevents it being moved any further up. SO, I know that I can attach it to the seat post, but I'm wondering if I should, or more importantly why I shouldn't... Any help gratefully received.