I don't think you've misunderstood the option at all. Post-apocalypseical magic torn worlds are right up there with regular old magical fantasy worlds. Thats why we split the magic and genre options.
Genre: High fantasy/heroic fantasy
Genre: Mid fantasy
Genre: Low fantasy
Genre: Science fantasy
Genre: Steampunk
Genre: Science fiction
Genre: Post apocalyptic
Magic: High magic
Magic: Mid magic
Magic: Low magic
Magic: No magic
I don't think you've misunderstood the option at all. Post-apocalypseical magic torn worlds are right up there with regular old magical fantasy worlds. Thats why we split the magic and genre options.