Thanks for the comments, I'll give the 21x a try. If they do like the theme, but feel it's too stretched with a 21x, is it possible they'll ask me to resubmit with a smaller grid? Or would they just say "no, thanks"?
To be clear, what I send to Will will be my third set of three, but I'm no stranger to rejection. Having spent several unsuccessful years on the orchestra audition circuit, I'm used to it. It still sucks, but I know it's just part of the game.
There are, however, a couple things that do concern me. Specifically, the last time the WSJ published something of mine a couple years ago, I inquired a little too soon, maybe around a month after acceptance, when I might expect it to be printed, instead of waiting for notification (I was hurting for cash at the time, and I needed to know when I'd see the check). I think my faux pas annoyed the person who responded, and although I apologized profusely, I worry I may have damaged my reputation. Also, despite what I said earlier about rejection, if I submit puzzles that continue to get rejected, at least when it comes to NYT, I worry that my name might become synonymous with work that's never quite good enough, hurting my chances of success going forward. Maybe I'm just thinking about it too much.