getting called out on a thread that is over a year old.
gotta love it.

anyway, what year bike did you ride that you only got 63 mpg with?
My zx6rr (599cc) got between 50 and 60.
what it totally up to date on maintenance?
How many miles did it have on it?
What kind of oil do you use?
Hell, chain lube makes a big difference, especially when you are working with so little torque to begin with.
Did you have the suspension set up for you, or left it stock, or did you have it lowered?
Riding style has a LOT to do with the kind of mileage you can get.
What most people consider to be "conservative" I would call "getting on it too much"
the Kawasaki website says that the 250r should get 60+ mpg being ridden by an average rider.
Take some care into the bike itself, and take care of your throttle and you ought to be able to easily get more than that.
Most of my riding on the 250 was interstate, avoided busy times on the road, accelerated very conservatively, didn't ride out every gear like so many people do, kept the speed and more importantly, the rpms at a reasonable point.
The problem most people have with riding a bike, 250 or not, is that most people think you have to be a in certain gear at a certain speed, and therefore, they ride out 3rd gear when they are going 35-40 mph. They also accelerate faster than everyone else on the road. Same with the interstate, they want to blast down the road, but when you are dealing with traffic, blasting down the road drinks a lot of gas because you constantly have to slow down and speed back up. Accelerating from 50 to 80, in a 250r, takes a lot of throttle.
If I still had the bike, I would record an entire tank of gas for you so you could see it for yourself. I'd average over 350 miles to a tank.