What a fine speaker (and review)!
One thing I think is interesting is the evolution of thinking on cabinet diffraction by the more technically competent speaker companies over the last ~15 years or so. If you look at the speakers that represented top-tier engineering back then - e.g. KEF 20x/2, Revel Ultima, Vivid, TAD and Pioneer EX, NHT xD, GedLee, Grimm, JBL LSR 6-series studio monitors - they were all quite curvy or often had big roundovers or highly sculpted baffles.
Compare:
I'm not sure there's a 90 degree angle or for that matter even a flat plane on our Revel Gem2's! But today everyone except Genelec and Vivid seem to have gone boxy: 201/2 to Ref1/Ref1M, Revel Studio2 to F328Be, JBL 6328 to 708, and so on. While fashion, production costs, and bass efficiency (cabinet volume) play into that, what's notable to me here is this boring box shape with nothing but a slight waveguide around the concentric driver does not seem to suffer notable from diffraction effects.
201/2 is still IMO the prettiest speaker KEF has made to date though. My wife would probably prefer this one, albeit with a full-face grille.