Mine has the same problem, but mine starts going fast after 1/2 a tank and as soon it past 1/4 a tank my car seems to have more boost. But I usually I fill the tank before it gets to 1/4. I think it has to do with the fuel level device in the fuel tank itself. I think it reads it to slow in the first 1/2 tank and catches up to the remaining fuel in the tank. Thus looking like you are consuming more at the end of the tank.

Just my theory. Not sure if its true.

My ride(Cardomain link) : '95 Contour 16V Zetec DOHC, Teal , ATX Born on Sep. 4, 1995 86+ miles *LEDs mods are on their way!*