I can't imagine averaging 28 mpg unless you simply refuse to allow the battery to do its stuff. I don't drive in a city often. I did this weekend drive in Charleston WV, which is no Chicago or NYC, but after an interstate drive from central WV I was averaging 41.5 when I got to town. I was able to get it up to 43.9 driving around town at less than 25 mph. On the trip home my average was 40 (elevation difference) and the overall tank was around 41. Yes I did drive slow and worked to hit the number, but it wasn't that hard.

I still find myself accelerating, either on rural roads or interstate, and will look at the FE gage and see a number between 25 and 30; then I let off the gas and lightly reapply and the gage drops to 40 to 45 and didn't drop speed.

To get the best numbers you have to pay attention, to get 28 mpg you'd have to let a teen ager drive it.