It is based purely on my assumptions and observations.
When the tank is say 3/4th empty, I have to drive very carefully and sanely for a much longer distance to increase the FE on MID by even a single decimal place! Whereas it was a matter of few KMs when the tank was almost full.
My Trip-A has never been reset from Day-1. It shows an FE of 14.8KMPL. No matter how sanely I drive, it doesnot changes the FE figure over few KMs.
My Trip-B is always get a rest with a tankful. Initially it gives till 18-19KMPL, then gradually sits at 14-15KMPL. After using the fuel to an extent, it's very difficult to make it show a bigger figure.