FiTech EFI system

Starting the install of my FiTech EFI system and directions for O2 sensor says to install 2-4" after header collector. I can not install there due do my exhaust set-up. My options are install right in the header collector or approx 10" from collector.
What say you??

I installed mine in collector about 2 inches from end. It works good. Make sure you have no air leaks.