I don't worry about it too much. I'd rather drive it how it was meant to be driven.
I suppose i get around 300 miles to a tank on average, but it does vary a lot depending on the weight of the right foot !!
Hey if we were all worried about mpg why are we not driving diesels. Mind you they do make a lot of sense for every day use.
I only use my coupe at the weekend, too busy working during the week and driving my vivaro (diesel)