try to get jsut the very front of the packer stuck on the edge, so like on the corner, otherwise its a bitch, but just keep trying, sometimes it will just stick, the middle of the packer, lengthwise, it the best place to kinda stick it there. but if your doing it on a corner try to just have the front of the packer touching if you can, the less of the packer thats touching the easier it seems to stick.