Hi Darryl,
So your Solar Edge is tied-in on the MP2-out side?
You could set your SE on voltage curve power factor control. If set on P.F. Capacitive, your bus voltage should lower a few percentage. Look here:https://knowledge-center.solaredge.com/sites/kc/files/application_note_power_control_configuration.pdf
Also when disconnected the mains from the MP2, your SE will not be controlled by the MP2, when Batt. SoC reaches 100% than SE remains producing power and will switch off at voltage too high. (but there is a work around for that problem too Multiplus II with SolarEdge integration application note may cause damage - #6 by phaseshifter )