put the primary just ahead of the cat and secondary just after. like within a few inches. no big deal.....the primary will get the readings it needs anywhere before teh cat....and all the secondary o2 sensor does is tell you that your cat is ok.
if you would have said it like that the first time i wouldn't of had to ask again....just saying it goes after the cat tells me i could put it down by the muffler and it would be ok, know what I'm saying? thanks though, my question is answered