Old Guy Crack-Pot Observation

[iiipopes]

Elephant - I agree with you. I had a node in the valve block of the Besson 3-valve comp I used to own. A dent in the primary knuckle between the 1st & 2nd valves kept the 5th and 7th partials from being flat. When I had a tech remove the dent, everything went flat and lost center. So I took a ball peen hammer and carefully added back part of the original dent, and everything tuned up again. I never could find what caused 1+3 C above open BBb to be stuffy, but it had to be something similar, since low F 1+3 intonated well.

We don't give as much attention as we should to the valve block and how that affects the nodes and anti-nodes of certain pitches. Congrats on finding your solution.