You're right, I checked the spacing between Esc and F1 but not below. Looks like the Ducky is 1/4 of a key while the B.87 is 1/2...
Gon NerD 108 looks to be right there but it has too big a gap between alphas and arrows and the Leeku mx3000 has an even bigger gap under the F row - I'm out of ideas.
You could always wire up a Teensy ++ like I did, though mine doesn't have backlighting

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