Where I live and drive in Utah valley is pretty flat, with a few exceptions. I think where you drive makes the biggest difference. My Passat will usually max out at around 47mpg, but I have had a few 51mpg tanks. I drive the speed limit (70mph), and make a reasonable effort to coast, such as when getting off the interstate ramp. On a recent roadtrip to the Northwest, I thought this was my chance for a 1,000 mile tank. As soon as I hit the hills of eastern Oregon, the average started to drop and never recovered. Easy on the pedal, and 98% highway, and the average wouldn't go above 50.
Not complaining at 50, but judging by fuelly logs from many others, and my own experience tells me not to expect more than 48-50 unless you have very special circumstances or drive very slowly. Both are statistical outliers and should be disregarded in any logical analysis.