“ The single biggest factor is how it’s driven”
Ok. How is it driven?
Low rpm, highest gear - probably around 45.. keep speed as steady as possible
When I owned a vw golf diesel with a possible 50 mpg the car actually told the driver how to press the pedal and when to not. With a screen on the dash.
So you had an uneven ride with a lot of coasting.
I averaged around 39 to 42. And always parked in the GREEN car spots.