Viana do Castelo
I use a house rule that does that. I think it's 9 to a zone and the 10th one will push the lowest ranked priority zombie one space out.
This doesn't seem very fun...
And what about those runners that you can't kill with ranged attacks because of the bigger guys?
And what do you do with tye Horde? Often we get 10+ guys in the Horde...