do you have a cel or anything? i would say trying a tune up, and cleaning some sensors, but since i am unfamiliar with what you have engine wise, thats as far as i can suggest. scan it and check engine load, o2 signal, and maf/map signals.
There could be a few things causing this, even a slightly clogged catalytic converter (if you have those) its off by a bit i would assume based on 1.6l specs. but check those few things and give it a tune, and let us know your improvements..
is the 12.5l/100km a long term average? how many tanks full has this been over?
my aveo 1.4 A sedan only gets 11L/100km or 9km/L in city driving,
highway i can get best ever at 14.8km/L only once after like 30 fill ups....just once discipline driving with baby on board so crusing at constant 90kmh in the highway only can get 14.8km/L = 6.8L/100km