I'm in the same boat as Mister_Smart_LA on this one. In my 451, I usually averaged around 35-40mpg... never went below 30mpg average. And that's not taking it either, or "highway" miles, either. I'd drive it like i stole it most of the time, and where i live, and the roads i take on my daily work commute, it's nothing but hills with the occasional stop light.
Same with my 453... except now i seem to average, more often than not, around 40-45mpg. I'll usually get anywhere between 240-260 miles before the 1.3 gallon reserve pops up on screen, and i generally can only comfortably squeeze about up to what amounts to around 7 gallons into the tank (counting what i'm pumping in and what the reserve gauge says is in the tank).
And i think it's kinda funny to say that a car "reliably" gets no less than a certain MPG... especially when the low is 28 and the high is 45. That's not "reliable" in any sense of the word. That's just practically the absolute rock bottom mileage you could expect to get.... which every car has a "reliable" rock bottom. I find it hard to believe you're getting 23mpg on a tank in a 453. Even with temps in the high 90's with the AC cranking taking my usual hilly work commute, I don't think i've ever gone much below 40mpg on a tank.