I was once told it's not good practise to top off modern cars the way you describe it. I'm not sure why, but I imagine it's because the fuel starts traveling through the vapor emission lines. I believe the head supplied in the tank with this high amount of fuel will drive the fuel into the vapor emission lines until it reaches equilibrium of height.

During fillup you should probably stop at a reasonable point and just be happy with measuring your fuel consumption average over a few fillups.

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95 E320 Cabriolet, 159K