Increased mileage is probably in your imagination.
Dont take my word for it ask an automotive engineer
 I've had K&N filters before.  I know how modern EFI systems, as opposed to carbs, work.  The only performance increase will be in full throttle acceleration, in most cars.
If you never put the pedal to the metal, you will see no benefit because the engine computer meters the fuel to the actual air flow AFTER the filter as measured by the MAF {Mass Air Sensor}.. and verifies mixture by sampling the O2 sensors in the exhaust.
Caveat:  you must bear in mind that the MAF gets dirty over tens of thousands of miles.  The oil coating used in K&N will make that worse.  When the MAF gets dirty, you may see some mileage increase because the computer thinks there is less air flow and injects less fuel... never much because the computer will trim the mixture based on O2 sampling.
Increased mileage is probably in your imagination. Dont take my word for it ask an automotive engineer
 I've had K&N filters before. I know how modern EFI systems, as opposed to carbs, work. The only performance increase will be in full throttle acceleration, in most cars. If you never put the pedal to the metal, you will see no benefit because the engine computer meters the fuel to the actual air flow AFTER the filter as measured by the MAF {Mass Air Sensor}.. and verifies mixture by sampling the O2 sensors in the exhaust. Caveat:  you must bear in mind that the MAF gets dirty over tens of thousands of miles. The oil coating used in K&N will make that worse. When the MAF gets dirty, you may see some mileage increase because the computer thinks there is less air flow and injects less fuel... never much because the computer will trim the mixture based on O2 sampling.