That would/might be true. Simply gluing the face flush with the sides would've been no problem.that would lead to edge diffraction issues. most people will not be able to detect this by ear alone.
They use an EV ST35 driver brother to my ST350B driver.
My Advents have grills mounted flush to the outer edges (at the front), while my Monitor Audios have grills that cover the front edges (and they're still in the boxes, I'm runnin' nekked). My Tannoy Reveals have no grills.
Might be interesting to look at where the speaker cones themselves align with the front "flat board". Or not.