Your screen is a little ermm dusty 
I have no idea how on earth your getting such good mpg... how many miles has your GTI covered?
Mine has nearly done 6000 miles but mainly motorways.. best I seem to get is between 39-45mpg over 41 miles. 
Yours is doing very well at that, so many factors make a difference.
Time of day re traffic levels makes over 10% difference too.
If you did my route I'm sure it would be the same.
Mines done 1.3k miles.
I had a Prius before the Gti, and was an anorak 'hypermiler club' nothing particularly ground breaking just all the normal tips combined.