Tigor giving poor fuel economy!

I have a BS6 Tigor Petrol and it has done around 47000kms,
I have recently started observing that my car is giving me avg. of around 12.5kmp/l in city. While some would say that is decent, well according to my driving style just a few thousand kms back I was getting 15-16kmp/l in city.

And I am driving in same city with same style so nothing has changed from my side, I also waited for few refuelings thinking it might be bad fuel but it doesn't seem to be the case.

I don't know what has happened or what is causing that issue...I read an article on Team BHP that it could be due to a faulty thermostat as I was also facing the issue where engine was not reaching its optimum temp. . I got the thermostat changed and that issue has been resolved but it didn't solve the avg. issue.

Anyone who could help, it would be great.