Third data point: Filled up today, 366.0 miles, a shade over 16 gallons, for 22.75 mpg. Again my usual 70% city driving, with 3 24-mile round trips to the 'burbs in the two-week period. Weather has been chilly, but not below freezing. The Average Fuel Economy meter said 22.9; average speed about 24 mph. So again, the car's meter is quite close to the fillup/calculation method.
I have to say I'm a little disappointed in the mpg of this car. To me a normally-aspirated 4cyl. should do a bit better than that. Maybe it's that I have to rev it some on takeoff. Now that I'm used to the way the Regal rides, I may try bumping up the tire pressure 1-2 pounds over the stock 33, and see what effect that has.