That sounds more reasonable and logical than my guess, but - even today - the huge tubas - in particular - seem to often miss the mark, as far as tuning range is concerned. The most common error seems to be making B-flat tubas for the American market too long, so as they barely play up to pitch.
There are some not-B-flat tubas - signature models - which barely play up to pitch and only with certain types of mouthpieces, but - knowing a little bit about the person associated with those signature models - I believe that's how they prefer to have their instruments set up.
I had an opportunity to purchase a huge Kruspe B-flat kaiser quite a few years ago from a local older gentleman, just a few years before he passed away. I would have to say that it looked like larger than 6/4 to me at the time, but that may have been due to my perspective and lack of experience with instruments unlike my own... I may have only been in my early twenties. It had the string linkage and the long paddles. I just didn't know how to make it go. Maybe it was a good instrument; maybe it wasn't. I think it ended up in North Carolina.
-----------------------------------------
Wow...
He and his wife must have been "conservative" or something...
They both (significant Memphis historical figures) have nearly been completely broomed from the internet.
She was the Music Director of the Memphis Symphony Chorus for decades. There's only a mention of her on the Memphis Symphony Chorus webpage, and her first name is misspelled, there.
I had to go to apolitical duckduckgo to find this
and this
duckduckgo also found this, which reminded me of her unceremoniously being fired, and then forming her own choir.
https://www.bizapedia.com/tn/sara-beth- ... orale.html
This last link also helped me to unconfuse my memory. I knew that she and Nick were not particularly wealthy, yet I remembered going to the mansion district on Central Avenue to try out the Kruspe kaiser B-flat. That previous address explains it: They lived in an apartment, in a building that was just about the same size/shape as most of the mansions - so as to blend in and to be zoning approved:
picture of their apartment building:
https://i.imgur.com/8Y72LOJ.png
Allow me to type their names here, so there might possibly be one more place on the web where their names are mentioned:
Nick Causey, Memphis, Tennessee
Sara Beth Causey, Memphis, Tennessee - Music Director of the Memphis Symphony Chorus