With you not changing your driving behaviour that also doesnt make sense. If you topped up twice a month, thats ~1400km a month of driving? So ~50km per day, which would mean your EV has to be charged every 150km?
The tank was about 800km so slightly above your estimate. The EV6 reports an average consumption of 19,58kwh/100km. Slightly above your very conservative estimate. In addition we went on holiday as mentioned so that affected my average.
Can’t say for sure but this is my measurable experience…