I’ve come to realise fuel gauges can not be relied on at all, the safest and most accurate way of knowing where you’re at with fuel over range is to ZERO the trip meter at each fill up, never partially fill but always fill to the top.
The fuel light comes on at 4 liters(1 gal) left, and your trip computer shows how many kms per litre you are using.
Simple math exercise after that.