Depends on how you have the string cable on. I try to put the short slot in the back but do it whichever way the cable(s)/string (on a single cam) will cross as close to the middle of the bow as possible. Also there should be a gap between the two where they cross if installed right (instead of them rubbing against each other). Don't know if it matters or not but on a single cam I also try to have the cable end of the string in the longer slot so it minimizes the angle or lean of the idler. Hope this makes some sense.