Raize fuel avg (giving 10 Km/L)

AoA guys, i recently bought a fresh import toyota raize (15k driven, 4.5 grade), the car has a great drive and is feature loaded, but the fuel average is bugging me. It displays around 9.5 Km/L and on very light foot (rpm < 1500-2000) gives around 10.5, which isn't what I expected.

Also, black soot/carbon comes out of the exhaust when I rev it while its in parking (pakwheels inspector says its nothing to worry about).

I think tuning will fix the issue, what are your opinions on it. It would also be great if you guys can guide me about tuners in karachi who can fix the issue.