Nothing new here to this old man...
All that I can say is "Duh!" to this one.
I've been raving on about the long B on my Selmer Series 9 "full Boehm" clarinets since at least the early 1960's, pointing out just this very thing. And, like Mr. Fobes, I too noticed the same thing about the bass clarinet. (How can you miss it, to be completely fair?).
I noticed the inconsistencies in the timbre of older Bb sopranos as a wee tad, and noticed (in particular) that Buffet instruments (of whatever model) had the wide difference between the C and the B throughout the universe of horns that I was exposed to. However, my protests (coming from a young welp) were brushed aside with "That's the way it is!" comments from the college students and the few pros willing to deign to note my existence.
True, modern Buffet sopranos have improved on this; true, some of it may be in the eye (or ear) of the player alone due to the different direction in which the sound is emitted; and true, my old Buffet range to low E bass clarinet in the Albert system most certainly did not have this problem. But, only I had enough confidence in what I was hearing to admit that it was true.
(This one was never tested in the "behind the screen" trials in which I participated in Springfield MO in the 1960's (we were mostly concerned with the infamous "A clarinet mellow, Bb clarinet more shrill" question), mostly because we had too few "full Boehm" horns to make a valid universe.)
Nowadays, the consistency between my B in the staff and the adjacent C (and for that matter, the A below) is occasionally cause for comment, but the improvements in recent horns (over the last twenty years or so) has erased much of the gap.
The ring of Play-Doh in the bell is a new one, however...