The closer the sniffer is to the head the more accurate the tuning will be. Some pipes have a baffle you can't get the copper tube through. it's only a 1/4 inch and that small of of hole will not mess up the back pressure or change the tune of the pipe (per Dyna jet experts that build the dyno) their's no choice, I've used a long drill bit to put a small hole in the baffle and run the tube through, some times I could get away with feeding the tube from the front of the muffle and then install the muffler on the bike, have never done D & D slip-on's so dont know. If you've just done slip-on you probably don't need the bike tuned. but the rev limit will stay unchanged. I would do the A/C with the super tuner and install the pre-build stage 1 map that would up you rev limit, no dyno and I'm sure you would be happy or if not let them drill the hole. you can contact D & D for their input, they dyno their own pipes and they would be glad to recommend the best way for you to go.
Enjoy the sound