That's what I love about these books, it's a universe full of holes - not awfully inconsistent ones, just gaps - and space to fill in. Questions left unasked and unanswered! Adventure to be had!

I am sure I got lucky for sources, in that Sosc (or at least Self) is formulated in a way that the works you read for it contain fascinating theories and ways of analysing the whole world (and by transitive property, Narnia). I am sure yours relate! They have themes, right? You can drag in themes anywhere.