I don’t have an answer for this. I know a while back there was a thread here on the forums that was talking about the Human purge in the volcano. The Votaries of Skelos, It’s listed as a 1 - 4 difficulty but never spawns in the volcano. It was acknowledge that there was an issue with the purge spawning any purge that didn’t have a 1 - 6 rating if there was a purge in that area that did have a 1 - 6 rating.
So 1 - 4 Difficulty rating purge will not spawn if there is one that has a 1 - 6 rating in the same area. I for the life of me can’t locate that forum post now. But from memory it was noted as a bug for review.
The server settings were level 6 when I did the second test, now for the record I don’t know what specific level purge did come, Could have been a 5 or a 6, there is no way to tell in game or at least I don’t know how to tell.
To answer the question all I did was changed the server setting from 1 to 6 and received the more intense purge.
My guess is that the patch notes and what is actually happening don’t quite line up and that there is some work that needs to be done to fix it. Whether the 2 systems of “difficulty” location and server setting are working as intended I can’t comment, I simply don’t know.
From my experience it seems that all the purges are at the same level when I use official server settings for level 6, they all seem to me to have the same number of waves and the same number of thralls in the waves. If there has been a variation I have not noticed it, in all the time I have been playing and testing.
Though I do think there may have been some recent changes made to the purge, the test I did this morning is the first time I have seen Human NPC’s in an Imp purge, so I may have to put it back on the table for more testing.