Thanks for the link to yours - nice stuff. Yes, you're right, it takes on a whole different character up higher. I was listening recently to a 1970s recording of Dexter in Tokyo, doing it in Eb. As far as I'm aware F is the 'original' key so I chose to record it there, and liked the way it gave a boldness to the tune lower in the register - which is where I tend to like to start ballads. My Nearness of You recording, though (see previous post on this thread - Lockdown Ballad #4) is higher up on the horn. Always good to notice how we can open up a whole different colour palate and set of improvisational choices depending on which key we start in. I've always tried to be a 'tone' player, if that makes sense, so the improvisational process is very much about connecting with the sound of each individual note rather than scales etc... which is why I appreciate your message, as thinking about key is a really important thing for me.
Anyway, I go on - but thanks for connecting with such an interesting comment