So car went in to the dealer yesterday and they have "recalibrated the fuel gauge". They were pretty hopeful as the range went up as they did this.
When it was collected it was showing 140 miles range, and now its back its showing 158 miles, and it would have been driven 35 miles, so perhaps gained 50+miles? I'll run the tank down to when it asks to refuel and see if its different 🤞.
Dealer stated that when the car is on the Reserve level it can have between 5 and 15 litres of fuel in the tank. I said that 15 seemed a high number.