@ tashkeel That are some great fuel averages on a civic!
i have city 2012 and have never been able to achieve more than 19.3km/l. I travel about once a month between sadiqabad and islamabad (round trip of about 1850km).
im not really a hyper miler but try to maintain my car's momentum and speed; i accelerate moderately-high when overtaking a slower vehicle (i hate ppl who slowly overtake a slow moving truck because they break the whole momentum of the cars behind), use gear braking along with low brake pressure and shift gears so the car remains in the 2000rpm ~ 3000rpm bracket
Here are a couple of fuel avg figures (with 100% ac with full thermostat at fan speed 1-2) that i remember based on actual fuel consumed vs distance covered (not the trip avg show by the car as in my case it always shows about 5-6% better fuel average):
LHR-ISB motorway, avg speed 150+km/hr, fuel avg: 12.3 km/l, tires: dunlop sp300 185/65/r15
LHR-ISB motorway, avg speed 140km/hr, fuel avg: 13.5 km/l, tires: dunlop sp300 185/65/r15
LHR-ISB motorway, avg speed 130km/hr, fuel avg: 14.4 km/l, tires: dunlop sp300 185/65/r15
LHR-ISB motorway, avg speed 120km/hr, fuel avg: 15.5 km/l, tires: dunlop sp300 185/65/r15
LHR-ISB motorway, avg speed 110km/hr, fuel avg: 16.7 km/l, tires: dunlop sp300 185/65/r15
LHR-ISB motorway, avg speed 100km/hr, fuel avg: 18.1 km/l, tires: dunlop sp300 185/65/r15
SDQ-LHR KLP road, LHR-ISB GT road (total distance: 910km), avg speed 80km/hr*, target speed 110 km/hr** fuel avg: 18.2 km/l, tires: dunlop sp300 185/65/r15
SDQ-LHR KLP road, LHR-ISB GT road (total distance: 910km), avg speed 90km/hr*, target speed 110 km/hr** fuel avg: 18.4 km/l, tires: michelin energy saver 195/65/r15
SDQ-LHR KLP road, LHR-ISB GT road (total distance: 910km), avg speed 75km/hr*, target speed 100 km/hr** fuel avg: 19.3 km/l, tires: dunlop sp300 185/65/r15
Some other factors besides driving habits that effect fuel economy based on my experience:
On avg the dunlop tires gave about 0.8 km/l better fuel economy than the michelin (185mm wide tires vs 195mm tires)
Fuel quality (fuel station, time of refuling, amount of fuel refulled etc.) also effects fuel economy (can be as high as 1.7 km/l)
continuous use of a/c decreases fuel economy by about 1.3 km/l
Car maintenance performed recently (air, fuel filter cleaned/ replaced, lube oil replaced)
road condition more bumpy = less fuel economy
and traffic density
*avg speed here is the avg for whole trip (i.e. total distance divided by total time taken)
** target speed is the constant speed that i want to maintain