Jeez, I guess I gotta get my geek-ness going.
Now all the sudden, I'm excited about running a few tanks in both cars to check the math versus stated readout.
I believe after both vehicles click off at the pump they take .3 to .5 more of a gallon to top off or 2nd click. That is my habit, so at least it should be fairly consistent.
.3 of a gallon more or .3 less takes my 20.27 mpg average to 19.95 or 20.62