What keeps the Rear window closed on a hardtop?

Hey guys, just wondering about the hardtop glass and what keeps it shut. I was thinking that the tail gate should keep it shut but mine tends to move past the seals and then rattle and makes my rear wiper catch the centre tail light when I go to operate it? I do have the brackets installed for it on either side. Does someone have a picture of the way it should look?

Any advise?

Thanks.