I am baffled. too. Don't see how it works: some (a few) lights serve both across and down clues but most don't.
On the basis of W maybe think of islands for theme?
the theme is islands...two answer for each clue each beginning with the clue letter, where to fit them is the problem though I think there is only one that can fit the right hand top corner and that is B [the only letter with a nine and a six clued answer