As far as I understood so far the efficiency is fixed to 90% per default. This is mentioned in the Node-Red Version: GitHub - victronenergy/dynamic-ess
I have a 48V System and my total efficiency is 80% (calculated from kWh counters in/out from VRM).
So I changed default efficiency to 80%. This can be done via dbus com.victronenergy.settings/Settings/DynamicEss/SystemEfficiency
I ssh’d into the Cerbo and changed it with dbus-spy (done in less than a minute).