Thank you so much Robert.
I now have the Mk2pvRouter supply wired via a loop that passes through the battery’s CT and, as you indicated this has calmed the whole system down.
With this new topology the battery’s web interface now shows an “export” amount when the battery is not absorbing all surpus power, but this “export” is then offered th the Mk2 - which seems to be much finer-grained and responsive in its diversion which is improving my total self-consumption.
So thanks very much for the suggestions, much appreciated, David.