So I've tried it and, while I did manage to get one note per beat, I don't believe that actually addresses OP's issue in retrospect, as one note per beat (4 quarter notes per measure) is actually more notes per beat than I would want in a solo that builds up gradually (in which case a long sustained note here or there could be tastefully played over even a couple of measures.

I also tried messing around with the phrase length setting, but the results were a disaster (although that may just be an issue with me not setting the parameters properly).

BTW, note that there is an option under the preferences settings for RTs to allow solos to crescendo (see screenshot), so make sure you have that checked (I do, and IME, it does not afford the flexibility and scope as envisioned by OP).

It would be great if PG Music could make a video about this by all means!

FWIW, there are amazing things that could be done under the hood in BIAB with RTs. I had my mind absolutely blown out of the water when I managed to generate a medley of RTs jamming out the solo for Hotel California using a saxophone, piano, jazz guitar, fiddle and slide guitar. The RTs I used (and you could listen to the "raw data" for said tracks as they sit in a BB sub-folder) had absolutely no hint of said melody, yet the program put it all together with the right parameters tweaked, which I consider to be the most insanely awesome thing about this program I've ever discovered. The implications and possibilities hinted at here are boundless.

You can hear the track here: https://soundcloud.com/user-423212678/biab-jamming-hotel-california-inspired-solo

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