So - on further investigation, looks like a bug related to Low Latency Monitoring.
Low Latency Monitoring off? Everything works as expected and I hear patch changes as I make them.
Low Latency Monitoring on? I can twiddle Helix Native's knobs until the cows come home, I don't hear any changes at all.
I'm assuming this is a bug (unless the view is this is a well known "feature" and everything is working "by design"...)