What a generous series of posts DB. And your original observation is very insightful. How could there not be an SOP for something this crucial. Let's hope there was here, and let's hope it's published in the final report.
Looks like roundwego is doing some research into the consequences of the Primus using the GMAP2 setting with 10nm range, so let's hope something good comes of that. It's suggestive that these settings are specifically referred to in the report as increasing the amount of clutter on the screen, and it was a high seastate night.
Would still love to know from users of this sort of kit what a rocky outcrop looks like on radar vs a distant headland. All the radar energy from any point in the scan's azimuth will come back from a very narrow range which the screen ought to interpret as a rough coastline rather than as a blob. And there should be nothing at all behind the coastline as it's in radar shadow. I think someone else was talking about this earlier.
Very hard to see how you could miss a feature like that and yet spot a generic blob at 6nm. But as they weren't expecting a rock, maybe they just tuned out or rationalised the echo as something unthreatening.