Believe it or not, most automotive fuel indicators act in a non-linear fashion by design. I would expect the Contour is not exeption. I worked at Visteon for a spell where we manufactured fuel delivery modules for Rangers and F-150s. My experience is that there is an algorithm that determines needle position based on input from the float mechanism. This algorithm takes into account several things: 1) it dampens fluctuations due to sloshing of fuel and 2) Customer's expectations--meaning a driver wants to see the tank as "full" for a while after filling up. Also, a half a tank gives the driver a feeling of security, so it tends to dwell there. Once the tanks starts to run down, it moves to "E" rather quickly, presumbaly to give the driver ample warning that fuel is getting low.
In other words, the behavior that is being described most likely is intentional...
