I would suggest to pay more attention to the fuel light
Accuracy is limited by the given circumstances. The fuel sensor does not give a distinct signal for every fuel level. Instead it is a combination of 13 switches with unequal spread. The lowest switch point is at 4 liters. Hence at steady conditions it can be anywhere between 0 .. 4 liter. You only get a more precise "estimation" by averaging if the fuel flows around.
You could try to fine adjust the fuel readout with 2 parameters in the menu. There might be slight differences from loom to loom and fuel sensor.
Try to adjust "fuel sensor offset ohm" in the extended menu. It is set to -6 by default (for to compensate several effects). Lowering the value shifts the internal correction curve to show lower values.
A better way would be to eliminate the root cause and improve the grounding of "the front", and by this for the fuel sensor. Add an extra ground cable at the headlight bulb connector and route it to the next possible point of the frame. In addition you could do the same for the ground cable going to the dashboard connector (black cable). Tab it and route to the frame. The old ground lines remain in parallel.