We already wrote in a german forum, but I didn´t know you are driving a Mini Cooper right now. I found your Spritmonitor profile (stating 5.0 l/100 km average with the Mini Cooper) and I think your improvement in fuel consumption could be much more than 0.5 liters.
As I wrote in the other forum, I get about 3.4 to 4.0 l/100 km on 10 km short distances in the summer. Mostly I drive the short distances with a passenger, there are some stops, too, and I drive about 70 km/h because there are not many speed limits. Long distances behind trucks result in 3.0 l/100 km in the summer, which is way below your 4.0 to 4.5 l/100 km trips on the autobahn. Even with air conditioning the Space Star would be much more efficient in my opinion.
Mitsubishi Space Star 1.2:
Daihatsu Cuore L251:
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View my fuel log 2015 Space Star Klassik Kollektion+ 1.2 manual: 67.5 mpg (US) ... 28.7 km/L ... 3.5 L/100 km ... 81.0 mpg (Imp)