[svandamme]

I'm saying, WHO CARES if it runs a smidgeon leaner at idle
the variation/error of measurement is to big in that operating state of the engine.
None of it matters

unless you are in some kind of lab.. that measurement can go one way or another based on any of the other variables of the day.. barometric pressure, ambient air temp, engine temp state, fuel temp

the fuel you put in
unless you can switch fuels at the flick of a switch and compare the AFR variation each time, on the fly, your measurement and comparison is pointless. It's within the tolerance of your measurement variation.