The Couturier's had conical tubing from beginning to end. The idea was one could get a better sound by having conical shape to the slide tubing. Thus, as you can see, the 1st, 2nd, and 3rd valve slides cannot be pulled for tuning. There is a tuning slide in the leadpipe and one after the leadpipe. I have never played one of these horns. If it is indeed high pitch, it would be virtually impossible to alter because you couldn't easily lengthen the valve tubing.
Adams E3 0.60 Sterling bell - Prototype top sprung valves
Concord Band
Winchendon Winds
Townsend Military Band