If I want to make a 120bpm 12/8 track play in Biab I have to set the base tempo to 80 and the main tempo to 80.
You should be able to have the chord entry per beat rather than having to enter a comma for two chords two beats so if you up the time signature per bar you can just select the beat and enter the chord.
I'm getting a headache thinking about it, I'm forever finding workarounds over the years, sounds like more worms, again just mod the BBPlugin I think.
It's like that as it was made for backing/learning and never thought it would be used to create songs/add tracks to a DAW.

Are there more users now that want it for tracks in a DAW or more that want a backing band ????

Watch https://www.dropbox.com/s/ca037ta73uhh6za/BB-Reaper-12-8.mp4?dl=0

Download BB-Reaper-12-8.mp4