Where to mount wideband O2 sensor.

So doing some work on my exhaust after the 5.9 swap.
Adding an Innovate LC-1 air/fuel gauge.
The instructions say to mount the o2-sensor 24" back from the exhaust port, and then it says (collector).

So does it mean in the collector, 24" from the exhaust ports.
Or
24" back from where the collector bolts to the header? That seems pretty far back.

Pretty sure I've read of guys putting them in the collector right after the header, but thought I'd ask for opinions before I drill holes and weld the bung on.
Running Doug's headers and 2-1/2" pipe from there back.