Hi Jazzman 1945,
When I open the link you provided, I only get one recording without a time line that tells me where in my recording the notes were taken from.
I understand subtlety in music, and I can hear and see some very minor variations in your comparison–and I can hear even greater variation over the course of my recording–but to me this variation is well within the limits of variation that can result from: inconsistent blowing pressure, position of the melodica near my chest, variation in the position of the melodica compared to the mic, my hand position on the back of the melodica, and few other things.
A true comparison would require close adherence to the scientific method and machine-like precision in playing and recording the melodica.
But even given the variables I did not control well, from a practical standpoint, I did not hear a level of variation that told me I should go out and buy big diameter tubing. [Though I am going to continue my exploration with large diameter tubing until I convinced the it has no beneficial influence on tone quality. And I am going to continue to look for my original recording that suggested large diameter tubing produced a more pleasing sound.]
Yes, no two notes ever sound the same. But I just did not hear a significant difference in my recording between narrow and large tubes that I would attribute to just the tube diameter alone.