Hi, Mike. Mpg depends far more on the driver and the route than on the vehicle itself. If you drive in the least bit "spirited", with regular acceleration and braking, or if your route is heavily urbanised, with lots of lights and stop sign, this all kills your mpg. Short journeys are a killer, as is speed on the freeway. Another factor is how heavily laden the vehicle is. If you regularly humph around items, unnecessary for your daily driving, you will kill your mpg.
You say it runs as sweet as a sewing machine. Is that because you use a heavier grade engine and transmission oil? What about tyre pressures? Are they correct and checked regularly?
All these things affect your fuel economy and can make or break mpg numbers.
2006 Honda Jazz 1.2i-DSi S Vivid Blue Pearl