Hello Levi501,
yaou are telling us already known things.
Just look on the left side to my Fuel-Monitor. Klick on the 7,2 Liter.
I fill my Smart with a very easy Calculation: 35 Liter minus the shown remain volume in Liter. Therefor i continue tanking after the click until i am ready.
You will see many more Kilometers than 200 in my "Fuel-Monitor".
PoWder
Sometimes i fill the car with 40 Liters minus remain volume in Liter.