I also have the same query .
When I gave my VVT Swift 1.2 ZXI reborn , from Mobil0W20 they had changed to ECSTAR0W20 (Came to know that ECSTAR is like a franchise of suzuki , and they use Idimitzu oil - Which I am quite proud to have used in my Activa too ) .
I drive 25kms one side daily in less than regular delhi's traffic. Yet this car is giving me just 17.5 kmpl without AC. my figo's 1.5 return 17kmpl in regular Delhi traffic with lots of short trips.
I guess AMT is to be blamed yet the brochure says AMT and manual mileage figures are the same as per ARAI. on this route any diesel car should give 20kmpl since 10kms of the 25kmpl is devoid of any traffic.
In regular traffic with ac this car returns between 14-15kmpl.