I have not yet deployed a UN to production environment. Currently working in test environment and trying to establish the subnetworks for our Water UN (Hierarchical tier). In many ways, the schema is very close to the ESRI Water UN Foundation database, which is what I'd like to point to for this question.
For creating subnetworks, I realize you must assign one or more subnetwork controllers as the point of entry, but what I'm not understanding with the ESRI UN foundation shown below is how System Valve / Pressure Zone features are the barrier points for defining a pressure plane subnetwork. In the network properties (2nd screenshot), it's Pressure Valve / Pressure Reducing features that are controllers. So where is it defined in the network to indicate that System Valve / Pressure Zone can also be a start/end subnetwork barrier? I don't think "Isolating" category is relevant for a pressure subnetwork. I don't see anything else, and cannot find any documentation, to know exactly how this works.

