On closer inspection, it appears that the problem is certain assets dropping any request coming from outside their assigned address range.
This appears to be a crude and problematic security "feature" and has been brought up with the manufacturer. If I can verify, I'll mark this is solved.
it may be necessary to configure as peer-peer and put each connecting client in the address range of the LAN, which, given we're using a class A as a classification system, there's plenty of class C ranges not internally assigned.
Will update with any progress.