I'm also getting better mileage than fuelly indicates. 2016 F150 4X4 SUPERCREW with the 5.0. 19,500 KM's on the clock and averaging 13.5L/100KM (which includes some towing), and that's with over sized tires (34.6"). My current tank with about 300 km's is averaging 12.3L/100km's.
Speedometer has been calibrated as well for the larger tires. As has been said, it's all in how you drive.