Sorry to not be able to add anything, but I have a couple of questions about spawning S ranks.

If you do the spawn conditions correctly, how do you know if it's spawned? Does it spawn instantly? Does it always spawn next to the person that caused it?

I've seen a couple of people mention "landmines" and "spawn points" here. Do all hunts have a few dedicated places that they spawn at or can they be anywhere?

Do we have any information on Kaiser Behemoth or Bird of Paradise? The hunter-scholar in the Sea of Clouds doesn't even mention an S rank in the area, so no story for hints. I've not checked Western yet but it sounds like a similar situation.