What is the limit to the number of people in a 1 entrance crouch spot, 2 entrance crouch spot?

I would like to assume that if there is only 1 entrance, 2 people is too many, but 1 is never enough, damn it, need 1.5 people, but anyway, 2 should seem plenty. With the speed and hp of some zombies, a zombie train on 2 people should in theory eventually win over the guns, but there are always stupid zombies. With 2 entrances, 3 people should be more than enough, mainly because the zombies are usually split up trying to get into both entrances.

The one lilpanic map with the double ended curved vent is always a problem, especially since people like to push a vending machine in as well as loading it up with 6-8 people. Just an example.