Also traffic flow, congestion matters a lot. Just before ramzan my Grande avg had fallen to 11.9, but as soon as Ramzan began office timing changed but not for me. I work on same clock as before so I get very less morning rush hour traffic because I make my commute to office, which is 25 kms away from my home, an hour before the other office goers.
I return just after Iftar and put my car on cruise control for at least 20 kms of the journey and now my fuel avg is showing 14.1
Such a difference can make traffic congestion on the fuel avg and yes short journeys, stop and go reduce fuel avg