Modifying Gumshoe One-2-One difficulties for non-horror campaigns

Cthulhu Confidential is very clear that its Challenge Difficulty Table (p53) assumes the game wants to achieve a horror atmosphere (of the dread type as described in Nightmares of Mine). The appendices (Player Characters for Other Mystery Genres, Generic Edges, Generic Problems, pp302-319) offer good support for running Gumshoe One-2-One in other genres, but I’ve found no mention anywhere in the book about how to tailor difficulty numbers for non-horror games.

How do a challenge’s Setback/Hold/Advance target numbers influence the mood and atmosphere of a game, and what rules of thumb can I use to determine the right numbers to evoke other, non-horror, genres?