location of a oxy sensor?

hello, car nuts.

picked up a oxy sensor for a 02 mazda miata ($17)
and a air fuel gauge for $14

yes, you should know what im going to do with it but, where to mount that sensor? running headers to h pipe to dump out at the axle (h is about foot down from collectors, too far?)

should i burn a bung in on the "H" section so its reading both banks, or on one side right after the collectors?

cant throw it on the headers, need to take the exhaust off so i can bring it to school to weld it all up. thanks and i will let you know how good this thing works. i think edelbrock wanted 200 something for this setup, i spent 30 :newb: