Thanks for your response, Kevin — informative as usual.
I noticed that the more I’ve been playing my new P-32D, the less trouble I have with the C key that was not always sounding. And I have worked on that note. The air flow in your melodica, though, is from the top down, pushing the reed toward the reed plate, right? So it flattens the reed in another sense, flattening against the reed plate and thus narrowing the gap. So does changing the gap tune the reed, flattening it by narrowing the gap, and sharping it by widening the gap.
When I commented about the gaps not being uniform, I meant that there were slight variations along the keyboard, in addition to the fact that the gaps increase relative to the size of the reed.
I got a Suzuki M-32C today, shipped from Japan. It seems very nice. I noticed a few things right away. 1. There’s no indication of where it was made on the melodica itself — My STUDY 32 is clearly marked “MADE IN CHINA.” The emblem on the case, though, says “M-32C Japan”, 2. It is heavier (at 759g) than The Yamaha P-32D (656g) and much heavier than the Suzuki STUDY 32 (597g). I know the tray is made of metal. 3. The C4 key has a “C” on it. This marking is the same as on my Soprano Mylodica, so I believe that The Soprano Mylodica has a Suzuki in it. I’ll write a review after I’ve used it for awhile.