I have noticed using the engine debug app that the fuel consumption of cars in this game is a bit off. Even in the 1.5L DXi covet, while barely using 15% throttle input and keeping the engine below 2000 RPM it somehow manages to slurp down 8 or 9L/100km, and if you so much as breathe on the gas pedal the consumption shoots up to 20L or so. For reference my parents' 1.4 Kia will consume 7L/100km at mostly half throttle at 2000 RPM. It seems these figures are a bit exagerated if you ask me.
the game isn't using average stats for fuel consumption afaik. it shows how much the car is using at the moment. no average thing at all. in real life cars it's only showing the average (and you're sometimes just letting the car roll , don't use the gas pedal much -> which results in an average of for example your parents' 1.4 Kia - 7K/100km). and cars on racetrakcs for example can even have an average of 40L/100km when you're like pedal to the metal 24/7 correct me if i'm wrong , but i think the app is showing the right fuel consumption.