I dont have the same issue as you, but 100% the fuel gauge and DTE read out takes into account how the vehicle is being driven at that very moment. Ive been out on track and the fuel light came on, pulled into the paddock turned it off. Few minutes later and on flat ground, the gauge went back up to 1/4 tank.
In previous cars with no mpg display id always reset the trip when putting a set amount of fuel in, so id always have a rough idea of how many miles ive got left in the tank. Maybe try that, then later when you get a good idea on how far combined driving style 10 litres gets you - the rest is east math *as a guide