MFD was showing a range of 1,300 miles with min/max required at 10.5 and 20.25 litres, so I topped up with 19.25 litres from the pump at my local Shell fuel station. At 149.9p per litre, I'm sure it wasn't the cheapest deal around, but it was the most convenient.
Upon restart, the range immediately updated to show 16,000 miles, so any concerns re overfilling or the sensor not detecting the top-up simply dissipated.