P-1prodrive

just wondered how much oil should be put in my 04 sti.always thought it was 4.5 ltrs ,but changed the oil today ,primed the filter,and the car still took just short of 5ltrs.that was after it settled, and on the correct top level, ie max dot, anyone found any odd reasons or can explain this, ohh ps, i was on level ground too, cheers pete.