AFE Bias in the Engineering Test mode (ET) can be adjusted so the computed MPG matches actual MPG. Decrease the AFE bias if the computed mileage is higher than actual. Increase the AFE bias if the computed mileage is lower than actual. ET Mode is activated by holding the left "OK" button while turning on the car (don't need to start it) until ET mode is engaged on the left display.
We did a 5400 mile road trip in the girlfriend's Malibu 2.0 turbo, and we were averaging 32-33 mpg most of the trip. Going from Yellowstone to Montana through the Beartooth Pass, we were averaging 35.5 mpg. Keep in mind this is a 3500+ lb sedan with a 260 hp turbo engine. Coupled with a 18 gal fuel tank, our range was well over 500 miles.
My Fusion Sport gets about 21-22 mpg average driving, and on the freeway I've seen 25-27 mpg for pure freeway driving. Keeping it at under 75 mph helps because of our gearing. Her Malibu is geared in a way that at 80 mph, we're cruising at 2000 RPM.
* 2017 Fusion Sport, 12.7 @ 108 mph tune-only (early tune of mine, bad trans settings), full trunk w/ lunch, and dirty paper air filter
* 2014 SHO non-PP, 12.4 @ 111 mph tune-only, all day long with dirty paper air filter and worn out 30k RS-As