That's not entirely surprising to me, Yapster. It's a bit like that my Peterbilt gets less mpg than my 3500, but not by a lot, despite pulling a heavier load. Heavier, but not heavy at 35,000 lbs. or so.The thing is a beast like the HC but you guy get as good a mpg as my SXT which I did buy for the mpg it gets.
Your small engine has to work harder than a Hellcat's to perform the same job, so I can see how the difference in mileage may not be very large.
It'd be very interesting to have an SXT and a Hellcat and go for a drive, keeping things as equal as possible, and see what the difference is after most of a full tank.
Or, if you could get a loaner Hellcat for your commute. I bet it'd be hard for you to keep your foot out of it, though.