from Nov to Feb a Cultus gives approx 135KM / cylinder fill. Aircon works during day.
from Feb to Nov the same car give approx 110KM / cylinder fill aircon is always on.
whatever comes from the factory in a car does not overload engine. after market stuff does.
2ndly for max performance on CNG the pressure at station makes the difference.
to my experience, best time for CNG fill is early in morning between 7 - 8 am & between 4 - 5 PM in evening. Thats when pumps have max of pressure.