Hi renault_megane_dci, welcome on board.
I have the scenic version (an MPV version) of the megane with the same engine and from the same year. My scenic is also 105HP but has 20.8 m.kg the weight is 1290 kg and both frontal area and Cd are more important.
My consumptions are 4.9 highway, 7.7 city and 5.9 combined.
As my wife and I are sharing our cars, I don't drive it often. This summer I was under 5.0 l/100 (over 47 mpg) on my daily commute. At Xmas I achieved a 4.41L/100 (53.32mpg).
I did a full front grill block (except in front of the turbo) which works very well to keep the engine hot and we had no overheating problem yet
but I'm wondering if for highway it isn't a little bit too closed...
These results were with tires inflated at 3.5 bars (51 psi), a lower steady speed and driving without brakes. In city I'm using pulse and coast in neutral (with engine on). Currently in the megane classic (our older car), I'm using pulse&coast at higher speed and I'm beating my summer results : 4.4L/100 (53 mpg).
Have fun,
Denis.