I wrote earlier about how to organize who stands where.
I just want to emphasize that there’s more at work here than just voice size and quality – and sometimes it’s just dumb luck that brings you to the best arrangement.
Almost any change you make will initially make things better. I suppose what’s happening is that people are so surprised by how different everything sounds, that there’s suddenly a lot more listening being done.
And it may just be by chance that chorus members discover that they hear things like timbre and tuning better with one ear than the other. I know that when I teach private voice lessons the singer has to be on my right in order for me to be able to do the magic thing when I can feel in my own mouth and throat what’s happening with their production. My right ear has spidey senses. There’s nothing wrong with the hearing in my left ear – I just seem to process the information quite differently.
When this is multiplied by the number of singers in a group, the potential for immediate improvement can be spectacular.
I’ve also received advice over the years to alternate the ‘leaners’ and the ‘leaders’ – or the people with forward placement between people with a naturally more dark vocal sound.
For now, I’ve come to the decision that people need to be told where their customary resonance sits – forward/bright, hooty/heady, far back/dark, or primarily chest. Armed with this information, they can play around with resonance till they match the singers on either side (https://betterchoirs.wordpress.com/2012/06/13/magic-choral-trick-156-playing-with-resonance/)
My other rule (for now) about all this is to avoid putting people with a big, really bright forward sound in the front row.