question

Concerning voltage itself:

The chargers are seeing two different voltages. The MPPT is seeing the true open circuit voltage reported by the SBS, and it also has multiple charge termination criteria - adaptive algorithm and tail current.

The Orion is seeing a higher voltage and entered absorption sooner. It is also a stronger charger, so it is inclined to drive the charging process.

Concerning multiple chargers:

When you have multiple chargers, the only time they can all function at max current is during the bulk phase. Once absorption is hit, the highest current charger pretty much runs the show. At absorption, voltage is maintained by only accepting as much current as is needed. If the MPPT were to try to add current, the voltage would rise. The MPPT sees that it can't add any more current, so it terminates absorption and drops to float.

The only time the above charger behavior doesn't happen is if the chargers can actually synchronize. Multiple MPPT in a VE.Smart network or the higher end VE.CAN MPPT can coordinate with each other to supply the same amount of current from each.

If you want to favor MPPT over DC-DC, experiment by lowering the DC-DC absorption voltage by 0.1 or 0.2V below the MPPT. This will help the MPPT to be the last charger running.