Apart from the fill level influencing how quickly oil goes down on the dipstick, oil will tend to remain in the crankcase longer right after an oil change. As the oil ages and begins to break down the engine consumes it quicker.

I have recorded this on my plane as well as on both the 8V92 and the Series 60. The first quart (on the plane, half gallon on the bus) will be consumed in half the time the next quart is consumed.