None of my thematic items at each of the clashes produces an integer when divided by 26 but the two word theme does. The preamble is a bit ambiguous here - "adding its letter values..." does "its" refer to 'one such item' or the 'description of the theme'?
Like ukridge I am surprised at the letter produced.
No one else is but i am struggling with 16ac despite having 3 out of the four letters: "to the west"?