It makes sense with normal reactors where you only need 3 connections, a fuel input, waste output and heat output.
These have 1 waste output, 1 fuel input, 2 pipe connections that you gotta connect if you want emergency cooling.
This pretty much means you can't make a 4 reactor system because you can't connect the ECCS to the top reactors just cause you don't have the space for an output pump
