Sr124 vented enclosure

wheely1up

So the polk page shows a vent that is 28" long , in a box that is only 26" long??? How does that make sense? Tech support won't answer my questions. Is it an L shape vent then? If i went with a dual ported, commom enclosure, they reccommend the port out the side, but i need subs and port facing in to the passenger compartment. I am cutting the rear package tray and fiberglassing through, in to the trunk. Are there any pro's that can help with this?