I don't see how the gauge could interfere with the pressure regulator unless it leaked to the outside (remember the occasional fuel odor with no fuel leak found).

There are 3 fuel lines connected to the regulator. The fuel rail is split-feed/split outlet, with each rail's outlet connected to an inlet port on the side of the regulator that is connected to a common chamber. The 3rd fuel line (bottom) is the return.

I check the regulator fairly often by observing the gauge at idle whenever I change the oil. I checked it on 2 separate occasions under load on the dyno and it was always smooth and steady.

Frank