I'm just really surprised that workarounds or fiddling with all kinds of settings are required to
get a basic 'This Masquerade' chord happening in BIAB.
It is 2024 right?
There's just one setting: Song Settings - "Natural Arrangements".
Here's another idea that should work well, and allows you to leave natural arrangements enabled (more natural playing with longer phrases)
1. Generate the track.
2. Song Settings | Natural arrangements - disable. (but don't re-generate)
3. Highlight only 17-18 and press F8 - generate new riff for just those bars.