I know this thread is a couple years old, but THANK YOU
I recently went stage 2 with cat-less DP. I was pretty certain I didn't have an exhaust leak - but when driving with any windows open even just a crack it would fill the car with nasty fumes.. I was pretty sure the vacuum of opening a window was sucking exhaust in from somewhere - but couldn't find it.
I found this thread last night and yelled "BINGO!"
I pulled the mat back, and went one step further than you. I pulled those vents out completely leaving just a gaping hole there.. I used plastic film and duct tape to completely seal that hole off on both sides.
Went to work today, got on the highway and cracked the sunroof - SUCCESS!!!! No more smell!! Thank you very much! You saved me some aggravation of trying to find a non-existing exhaust leak!!