Same here. I took out the breather pipe extension on my 75 litre tank (2021 Ducato) making it a 90 litre tank. So the fuel guage simply ignores the top 15 litres and treats it as a 75 litre tank. The gauge doesn't start going down until the level drops to 75 litres. So when your 90 litre tank is 2/3 full (60 litres) the guage will say its full. When your 90 litre tank is 1/3 full (30 litres) the gauge will say its half full. I find this easy easy to live with because I know about it. The important thing is it still tells me when I need to start looking for a place to fill up.
