I've got a dinky one for a maxi - a mere 10 litres - and it's sensitive to the terrain - especially when going down steep hills.
I generally get 120 miles before the fuel gauge flashes. When it's really low there's a yellow warning light too.
To fill it to the brim usually takes 7-8 litres and I feel psychologically 'happier' when it has a full tank.
The MPG is around 80 with the stock windscreen in summer and around 75mpg in the winter with the wind and the rain and the Fabbri screen fitted.

If you want to be incrementally better: Be competitive. If you want to be exponentially better: Be cooperative.