It's interesting, for sure, but I don't think it's a big deal. I've been excited over a sudden jump in consumption, too, only to then think it through and consider how many under/over-estimations I made to arrive at that figure.
If I had to guess, you are probably not accounting for any residual fuel in the lines, the bowl, petrol pump calibrations, etcetera. If you traveled 19.6 kilometers on 1 liter of petrol, could you travel 196 kilometers on 10 liters if it were a 10 liter bottle attached instead? Even 150 kilometers, or 130? Anything greater than your lifetime average?
Have you ever driven the car until it stopped in the middle of the road on 10 liters of fuel coming from your tank? What was the resultant fuel consumption?
Your number is only accurate if it is repeatable. I only consider my mileage to be 10km/L, for example, if I can get that number at least three times.
Maybe you have a magic 1 liter bottle. Try using it again.
