A couple of clarifications, offset is not a settable mode. It is a feature built into the inverter. Offset operates on 4 voltages, Absorb, Float, Equalize and the Sell RE set points. How it operates depends on the individual voltage set points between devices (inverters and FM charge controllers). Let’s consider a typical charging set point for an AGM battery. Typical Absorb value could vary from 57.6 to 59.6. If the inverter is set to 57.6 and the charge controllers (or external source) are set to 59.6. During a bulk cycle both sources will contribute to the charge of the battery. Once the inverters absorb value is reached 57.7 current flow into the battery is reduced. If the FM units have sufficient energy and attempt to reach their Absorb value of 59.6, charging from the grid is reduced to zero as long as its absorb value is maintained. Not only will charging from the inverter be reduced (possibly to zero). The inverter will do everything possible to maintain its absorb set point. If grid tied it will use excess pv to run the loads or even sell back to the grid. The inverter job is to maintain its voltage target be it the Absorb, Float, Equalize or the Sell Re set point. If a cloud passes by and solar harvest is reduced the inverter will use the grid to maintain the target voltage.