That is a great mileage you are getting. To be honest, I have not had calculated my gas mileage since I got my scoot. I usually ride the scoot for commute to work. Each leg is about 35-38 miles, not for sure, 100%. I do two round trips before filling up from a 5 gallon jug, which is use the gas for pressure washer and others.
Anyways, I'm thinking that I fill about 2 gallons each time for possibly 140 miles of riding, which makes about 70 miles per gallon with 165lbs arse.
I'm pretty happy with this.