I would bet that your poor mileage is almost entirely due to the short 2.5 mile commute (although that works in your favor as far as fuel consumption is concerned). I think I usually average high-20's for the first couple of miles on a cold engine, but I have seen as low as 21mpg (in 0 degree weather) on my own 6.5 mile commute.

If you want to rule out a mechanical problem, try a longer test drive (say 25 miles, on suburban or light-traffic city roads). At average speeds between 35 and 45mph, where you can take advantage of EV mode, you ought to see mileage numbers in the high thirties or above. Under those conditions, I usually see 45mpg.