K, do you mind me asking how you know 2d is 5 letters rather than 6? Has it been published as a correction? I confess I don't understand it at all. The clue works equally well, or better, at 6, and the symmetry of the entire crossword has been ruined for no reason. I smell the hand of an interfering editor, who either doesn't care for "is" in its shortened form, or doesn't like neckwear referring to more than one thing, both of which are surely uncontroversial. When we get weekly references to diacriticals and accents, thiis seems contrary.
I know it's an irrelevance to the solution, so I won't labour the point, but I would be most interested in your, and any other, views.