In 2 years I have never filled up with more than 9.9L / 100km. This has included driving ranging from bad peak hour traffic, spirited driving (ie set of tyres worn out in 45,000km) and highway miles. Tyre pressures at 38 front and 36 rear were typically used, but were adjusted based on driving pattern, tyre age and tyre wear. Not sure the dealer will be able to help very much with new information not mentioned above. As the dash always reads high numbers after refuelling, it may be suggest you to refuel (to 3 clicks of the bowser for example), drive 300 km on a 100km/h highway, with no load, and refuel again to the same number of clicks.