Thanks for solving!
4D is a letter bank clue - they're fairly rare in cryptics, but fun when they pop up. Basically the clue is telling you to take apart the pieces of 'tens' and rebuild them (repeating letters if needed) into a word meaning arrangements. This is a good guide to how they work, although they don't come up very often https://toughasnails.net/2020/07/27/decrypting-the-cryptic-11-letter-banks/