the average you get is about ok.
I had a manual civic 1.8 for a month and thats what i use to get (6-7) km/l in city.
as for Altis, I had the old Altis for a year and it always gave me 9-10 km/l in city (with AC) and 13.5-14 km/l on highways (with AC)
its a 1zz-fe engine designed for fuel econo and previous altis was lighter than civic as well.
new altis is (heavier than the old one i have heard) but has electronic power steering which helps in fuel econo.
on average i had 4 persons sitting in the car.
as to improve your fuel economy you can
1: check your tire pressure and adjust it correctly to the company specs, that will help for about 2-3 % in fuel economy.
2: replace spark plugs if you havent already.
3: standard size tires (recommended for your car) fat tires increase rolling resistance and drag, hence decreasing fuel ecomony.
4: soft throttle and shift to neutral in long trafic jams.
New Airfilter will not benifit you on petrol consumption (it is negligible)
a clean airfilter however keeps your engine oil clean so can change it after reccomended intervals.
you can Ask Cylestyne about the ideal consuption of civic though.