Could even be the tank has a small leak at that level. I would install a fuel pressure gauge and see how long it holds pressure after the engine is turned off. If it drops off quickly there could be a leak in one of the lines. As far as a leak in the evap I would think it would set a code. It is set up to find a .020 leak. Also check for fuel in the evap canister. May be sucking in fuel when you are full.