Some horrible suggestions for interpreting "top-line": 1. Imagine slicing off the very top of each of the capital letters in the grid. You get (kinda) a bunch of bits looking like - and .; divide them into groups somehow and interpret as Morse code. (So e.g. RAWER would be -/./.../-/- which could split up as -.. .. -- or DIM.) This is horrible because there are vastly many ways to split them up.

2. Write each letter in Braille and just take the top two spaces in its 2x3 block. Put them together somehow, and get a picture or some more Braille or something. This is horrible because there are too many different ways to put the two-bits-per-letter together.

Oh my, that would be horrendous. I promise you it's more straightforward than that by far!

I've added a hint of sorts. It doesn't give too much away just yet but it says you're looking for something much more visual. Interpret the missing piece correctly and it won't take you too long to solve it (no super-sophisticated analysis required!).

D'oh!

(haven't checked yet but I think I have it)

yup

done now

Oh, well done! That's the one!

Feedback welcome by the way on the cryptic clues if you have any more points you wish to add (but try not to be too brutal with me!). I've taken on board the points already raised in the discussion above (though I have no plans to create another cryptic just yet - it's purely a learning experience for me...). Thanks.