I have not read any of those, no—nor any Lovecraft or James. This is Hornung's only overtly supernatural book, so it would be interesting to consider what might have influenced him to go in that direction!

Stepping aside from the whole paradigm is the only way out.

Yes, exactly! And I do like that fic very much, and I think Roger/Gwyn does make an awful lot of sense when the book is considered this way.