I've been experimenting with a Horseman 451 6x9 back that I've been given. There's a problem in that the back seems to start "numbering" the frames too early, meaning the first frame is still mainly the paper backing and the last part of the film isn't exposed at all, meaning it's effectively only a 6 frame back.

Can anyone tell me what I'm missing here ? Is there a special way of loading the film ? I searched online for a PDF manual or equivalent but couldn't find one.