Average of New Petrol Ertiga VXI 2018 is just 11.0

Average of New Petrol Ertiga VXI 2018 is just 11.0 During my Test Drive I had observed that the average displayed on MID is just 11.0 which is very poor. Where as company claims that average of New Ertiga is 19.25 some where. Sales person at showroom said that vehicle will give average of 19 if the fuel tank is full, if fuel tank is half average will go down.