Replying to Adjusting Marker Griffons?

Well, A few binding problems recently, I have marker GRIFFONS, when i was trying to clip into my binding i noticed that it could slide along the rail if i applied a bit of pressure, is this supposed to happen? and if not how do i get it to stick in place?  second of all, i used to have a bsl of 317mm, and had my bindings mounted for them, but now I have a bsl of 302mm, and somehow ive tried moving the heel as far back on the rail as it'll go (by sliding with my hand) but it barely fits, how is this possible? :S, is it something to do with one of the screws? as in my old binding i was just to stick a flatea screwdriver under the latch and lift that up, but theres nothing like that with my griffons? Thanks a lot!