Se-Saloons in City max 7 - 8km/ltr, with AC or without makes no difference, it has a worst of fuel ave thats one of the reason it sells cheap.
Same is the direction for the current 1.6 Altis --- no doubt CVT is the future for combustion engines with better fuel ave.
Since its been driven on CNG -- better fuel ave can not achieved. Lot of desi mechanics will say I will fix it, I can promise it but no use.