I agree that the 1:1 ratio is a bit over the top. At home I had, and will have one box for two cats. At the moment I'm living with my GF so we have 2 noces for 4 cats. It's all fine. As Marcia mentioned, a lot will depend on how the cats get along. In my case all 4 are fine together.
I always recommend not putting the boxes all in the same room also. If one cat is guarding a box, they will be able to guard them all, and defeat the purpose. And oftentimes, us humans don't see that kind of behavior, but it happens.