These newer vehicles are pretty annoying with the dummy lights coming on effectively at 1/4 tank. My Ram has a 32 gallon tank and when the light comes on it will take about 25.5 gallons. This issue/problem has been beat to death on some Ram boards and the manufacturer has actually done a software update that should make it more realistic.
There's always talk about them doing it this way to keep the fuel pump submerged. It's also done so people don't run out of gas. Either way it's pretty annoying to not be able to really use all my gas without the fear of running out.