Hey, I just posted my own entry to the recorder competition too! It's in this forum as well. Haha... funny I just found this. The deadline was moved to August 15 for the competition if you'd like to lengthen your piece or revise it. You have plenty of time.
So that said... I don't think the "tuning" of a recorder will affect this at all. It's not very drastically relient on intonation. Yes, they are "just" and not "well-tempered" ... but that doesn't mean you can't use modes in just temperaments. Besides, we can adjust our airstream in just the tiniest bits to sway the intonation however we like. Sometimes we can use completely wrong fingerings that give an out of tune "rustic" feel to a note or two that has alternates.
I don't think the issue with this piece was as much the tendency to mix tonal and modal idioms... "tonal" is modal anyways. Ionian mode, you know? Very similar concept. The only things that bugged me about this piece was some of the rhythms didn't seem well thought-out. Measure 32 to the end was delightful, but 18 to 21 seemed a little random and 22 to 31 seemed a little uninteresting.
Hmm... dynamics? The recorder has a hard time with dynamics. If you try to play more loudly you blow sharp, if you try to play more piano dynamic, you end up flat... I really don't like to use them myself. For instance, the piano at measure 12 would not really be possible, in that range of the recorder there are pretty much two dynamics - on and off. That is... without fingering sharp and underblowing or some other trick. Maybe a professional recorder player could enlighten us on that, though. Maybe fingering nuances can help the matter a little, I have no idea. I'm only self-taught. At measure 22, however, I can actually get the dynamic contrast a lot better. It's really odd... I can't really tell where dynamics work without actually trying them myself on the instrument... it's a pain.
It's a nice piece, but I DO think you could improve it a little. And by all means, PLEASE keep writing for winds! You'll get better and better at it, and they're a very fun family with a lot of diversity and interesting techniques available.
