Cyrix and MPPT controller

I’m going to install a Victron Cyrix VSR on a friends boat. I’ve done it before - easy and no problems. However he has solar (Victron MPPT controller) and a single output battery charger (all batteries SLA), so he will get the benefit of spreading the solar and charger across both banks.
My concern is that the solar will (most of the time) be generating enough voltage to close the VSR and therefore every time he starts the engine it will be drawing from both banks. Also his domestics will be drawing from both banks even without the engine running or the mains charger being on.
Am I worrying about nothing?