I got 18.2pmg that was over a 8 mile strech... just roundabouts and 3 sets of lights
I'll try and re-create similar circumstances ....

And just to add..... a taxi!!! not to be underestimated in the I drive sooooo sloooooowly when i dont have a passenger, yet like i nutcase on crack when I do stakes 
R32UK, Gave it an urban run for 13 miles including a prolonged spell at 90 (kph
) in 3rd...
Couldn't get below 21.4mpg
Good form fella!!!

Atleast you gave it a good try. tbh when I push along to similar speed I would with the R im getting only marginally better mpg. It seems waiting for the turbo does really kill your consumption

(im guessing the engine is still quite tight yet also)
On the plus side if you drive like miss daisy and follow the suggested gear changes you can get very good mpg.