Most people place them on the hot pipe (before intercooler), but i put it on the cold pipe (after intercooler, right before throttle body).

I asked that same kind of question, everyone says that it doesnt really matter, but if you want to get super sensitive, just put it on the cold pipe. Having it near the throttle sort of makes more sense to me . I dont know how to explain it because i just woke up, but someone here might.