Here's what I see at that link. Try a private browsing window, that will clear login cookies and such.
I'm not completely in the doubter camp, I do think there's gains to be had, but ~8-10% or so is quite a lot. I remember there was a challenge a while back where a team drove a prius for a whole tank and hit a crazy tank average like 100mpg. I don't recall if it was a stock car or not, it was driven at more ideal speeds (25-30mph average I think), no radio, windows up, hot day, etc.
Didn't realize you had a full boat tail and such. You could easily hit those goals with slower speeds =). I'm running a nearly stock prius 45mph and for any kind of longer trip I'm hitting 55mpg or so, just have a grill block and missing a couple bell pan panels lol.
It looks like you live more in the city, I suspect it's more shorter trips for the car and such. You could probably see some big gains from a block heater, trans heater, etc. My MPG is horrible when the car is cold. It starts off around 30-35mpg and climbs at 40mph. There's also a mod to spoof the temp sensor to help get it to turn the engine off a bit sooner and such, I haven't messed with it but read about it. It currently takes my car around 6-7 miles to come up to temp.