Well I own the same car and it gave 9 km/l on AC strictly in local while its gasket was a bit blown.
The best bet for good mileage for this car due to 4 speed AT is to drive very mildly on 4th gear (overdrive) which is about 63 km/h on this car. By doing this I get 12 km/l without AC on a sub optimal engine.
These 4 speed AT paired with 1000 cc 1SZ-FE were not designed with consumption in mind so do not expect wonders. Manual version of Platz does around 16 km/l though