I fill up to the top when I do the supermarket shop. I can't be doing with the faffing about and filling with lesser amounts because I'd have to go out of my way if I did that which would defeat the object of the excercise. The exception would be on a day off and we're off out long distance and out of 'synch' food-shopping wise.
The supermarket is about 3 miles or so away and off a busy road. This being Sheffield, there is always the hilly terrain to be taken into account. I'd have to queue uphill, having just fuelled up, stop-starting. So it makes no sense to do this more often.
Off topic, but out of interest, I would imagine the average mpg in Sheffield (or anywhere else with similar topography as opposed to just 'size') is not as good as many cities or places that are flat. I do recall reading many years ago, possibly 1970s, that bus manufacturers used to put slightly larger engines in vehicles for South Yorkshire Transport, as it was back then, due to the steep gradients.