Turbo Engine mileage is bad

I have Bought Zeta Automatic. driven on the highway for more than 1500 km. Highway mileage was ~13.8. Never went above 14. Detailed Review -- 1) Driving Experience -- Better than Nexon AT in gear shifts. peddle shifter helps in overtaking, but still acceleration takes time(your mind will doubt and worry if the car will accelerate on time). Very comfortable in long drives, no issues faced. The turbo engine gives good power. 2) Driving View -- Seat adjustment helps, but I felt the blind spots are more, due to windshield mounted rear view mirror. 3) rear Seat belt warning -- Even if no one is seating, the warning beep continues for 2 minutes. 4) Mileage -- Biggest pain point for me. If you don't have a light foot. you will not get good mileage. NEXA should have given driving modes to control mileage(economy mode). My mileage which was ~13.9 after highway driving is now 12.8 after ~200 KM of city driving and is declining.