I'm not exactly sure I understand the question, but there are 2 positions that the knife holder can fit in on the tool carraige. If you want to perf cut over the channel instead of the cut strip, make sure that your blade holder is installed in the front position (this takes quite a bit of unscrewing of the thumbscrew that holds the blade holder in). If you want to cut on the cutting strip, then the blade holder should be in the back position. I hope this helps.
Good Luck