A guy by the name of Jim Smith has been advocating a speaker placement width of ~80% of the distance to the listener. Works for me.
There is more to it than that as others have mentioned.
https://www.youtube.com/watch?v=BOrZEreKB8Q
There is more to it than that as others have mentioned.
https://www.youtube.com/watch?v=BOrZEreKB8Q