Well technically, there are a few spots in places like mercenary Park and the desert map that have places that work best with two sentries and two dispensers too, for that matter. This is because X × the amount of ass you've eaten = that in mercenary park, it gives a tactical advantage. Especially if you have three engineers. Two normal sentries and a small sentry. Y × the max amount of team members ÷ the amount of racists are in the server will show if you should or shouldn't build a sentry next yo someone else's.
