My Suzuki Cultus 2018 fuel average in city is pathetic

[pwuser159895957528]

Car's data
Model: 2018
Varient: VXR
Mileage: 85000KM
Fuel average on long with A/C: 17-18Km/l
Fuel average city with A/C: 9.5-10
I get maximum of 350km on full tank (30-32 litres)
After 65000KM fuel average decreased till now
Currently Running on Shell Helix HX6 10W-40
Catalytic recently cleaned
New Spark Plugs on 75000
Regular maintenance is done on time.
Everything is clear while attaching OBD-II reader
What could be the reason?
Driven 20000KM with 9-10 km/l average
Fed up from the past 1.5 or 2 years.

For reference i have another Cultus VXL 2020 model
Mileage: 100,000km+
Average in city is 16-17 with A/C

[aminjafer5441]

Something is wrong and probably the catalytic cleaning has made it worse.
Try changing the oil grade to 5w30 hx7.
Use an in tank fuel system cleaner like liqui moly and pour it into full gas tank. Then drive aggressively until the tank of petrol is consumed. Or next time you hit the highway then use the fuel system cleaner.
Get your AC checked. It is causing any extra load on the engine due to low refrigerant? Block or clogged condenser will also cause the AC system to over work so have that cleaned with pressure water at a service station.
Rest a checkup from a good efi electrician might be required