just throwing it out there as you kind of called me out about the mileage....
and from my limited knowledge... after all, I am just a polish farmer.... most target WOT AFRs are in the low to mid 11's (11.3 - 11.5) so I would say if you are in the 12's, you are running a bit lean, and on the opposite side, if you dip into the 10's, a bit rich. tons of other other factors to consider, but just generalizing.