I think it's my description that's lacking. It's exactly the same problem with this (saw it only after I started this thread), only that my problem is with the suspension mechanism rather than the seat clamp. I'm still kinda new to biking terms so please bear with me.

I just had a look, both of my bikes have 27.2mm seatposts. So I guess I'll buy two of them so that I can lower the seat further for my friends to ride. It's not a problem with me, but my friends are a lot shorter