So yeah, if anyone's interested. I got 14.5 again on the last tank (all regular).
This time around i've refueled it with 25 % high octance, and the rest is regular.
Also, someone has advised me that in order to get the high mileage on these cars, the gears have to be changed really quickly, essentially, 3rd gear when it's doing 25 miles per hour. 4th at 40 miles etc.
So, i've been doing that, and going a bit easy on the accelerator. I think my fuel efficiency right now is around 20 km's which is great! This is just a wild guess. Will repost once the tank empties.