If you have zero load on the shunt it should display 0 amps. So when everything is disconnected or off and you press calibrate it sets whatever it is reading to zero.
The current threshold can have no impact depending on your system, my boat has about 1A draw minimum when moored and unused so it is always above the threshold apart from at dawn and dusk as the solar balances the load for a minute or so.
The other question I should have asked is how often do the batteries get fully charged, every day or less frequently. The longer the time between full charges the larger the accumulation of errors in the SOC. Maybe over a week without a full charge, the charge efficiency of 95 vs 99 could accumulate a 15% error.
I am on a boat that is not keeping up with the Starlink demands of working on line, so they have not been fully charged for weeks unless I used the generator. Sometimes the AC charger went into float mode when there was a 120AH defecit! The solar and 30A AC charger going into float prematurely has prevented full charges.
I am now back at a dock and able to plug in to shore power. Yesterday I input the settings as directed on the Victron Energy forum and plugged in the AC charger. It was in absorb mode for a full 10 hours and accunulated 43AH, although the fridge and parasitic loads were drawing on the batteries suring that time. I synchronized the batteries this morning, unsplugged from the charger and turned on the solar. The solar went into Float mode immediatly. Presumably because the batteries are fully charged. I will be watching to see if the solar is able to switrch to bulk or absorb mode as AH are drawnfrom the batteries.