Artistic license probably, also could have been so someone in the middle could add coal or what ever fuel they used in cycle.

We know they used techniques like this back in antiquity but we don’t know specifically how such foundries might have been setup. The artist might have been trying to show a very ad hoc setup.

Possibly so someone in the center can feed coal into the tops? They do seem awkwardly clustered even considering that, though. May just be the artist trying to fit as many as possible in a small space.