It's to do with fingerboard radius really...................a vintage radius board of say 7 to 9" is quite curved and the stagger seems to suit this and almost match the radius.Anything flatter than 10" and a stagger can sound imbalanced as some of the poles, particularly the D/G , are closer and others ,especially the B, further away.This is where a flat profile magnet balances the volume string to string much better.