What's the absolute maximum range of your Duster?

Today I ran my Duster out of fuel, then completely filled the tank and filler neck with gas. I was able to put 15.1 gallons in. My tank is a new 16 gallon tank. How many gallons does your completely empty Duster take? There must be an air bubble at the top of the tank that prevents the tank from being completely filled. By the way, completely running my tank dry gives me a range of 227 miles, calculated at 70 mph and 14.7 mpg. How far will your Duster go on a tank of gas. I'm surprised at how little range my car has. What do you think?
Cruiser, I get between 10-12 using non-ethanal 92. I always fill mine it back up at 1/4, ran out of gas too many times by pushing it. Carry a spare jug of fuel for your trip.