The problem with people claiming their MPG is the whole worlds of varying variables. A person is a flat location will get better MPG than one in a hilly location, Also the altitude matters, and rather or not they are using a/c too. And what speeds? Alot of people claim this and that mpg on the highway but offer no speed, a/c on and off, drafting, no drafting.
I personally get 18-19 in City (very short trips to work with 3 red lights, mostly flat) 17.7mpg round the area if I use the a/c fully, (I life in Chattanooga so there are many hills and steep climbs) On the highway @70 mph I can get upwards to 31mpg, 35+ with drafting (even with a safe following distance one can draft) Above 75 mph my mpg go to 26-28, and last time I was at 90mph, I got a reasonable 22mpg. I do notice I get somewhere between 1-2 mpg less if I use my a/c on the highway vs windows down. This is all calculated by my OTIS. On long distance trips where avg speed is 80mph, 26.6 seems to be the overall avg, (not resetting for stops or anything)