I will just shut your mouth with the following few posts. Unless of course you think all of these people shit mathematics and are making weird claims.
Notice the average of 14.5-16 on speeds of 14-150 in the last post. It seems to me that you have probably never driven a Grande. I can get you 15+ on a Grande even inside city, no matter how painful that drive will be. But the point is, it is very doable to get 18-19 kmpl on Grande on 100 kph. If you drive at 70kph constantly (I know its not practical), you can get above 21 kmpl easily.
Also, smaller engines on heavier bodies give worse fuel average than bigger engines on the same body. Your GLi will never give as good an average as a Grande on the same speed while cruising on motorway.