They are (I have come to realise) just far less so, but that may be because of the relative listen times.
Streamed R4 for 30 hours non-stop to an MS600 without the ethernet over power plugs involved; the stream restarted gracefully twice. So it seems that it is not a BBC capacity or BT HH problem (probably).
Streaming R4 to the 818 and at the same time streaming to Control:PC on a laptop connected to the same dumb switch after the ethernet over power plugs. The 818 lost connection but the laptop continued - which seems to eliminate the power plugs.
When the 818 loses connection I have noticed it briefly drops off the Control:PC zone list on the top right.