I've very rarely seen this type fuel system but I would've expected fuel pressure to alter in live data (direct injection system isn't it) under different engine loads as I'm sure the one I had in altered fuel pressure from idle to WOT.

On my problem car it was over pressurising due to a faulty regulator and the actual compared to desired fuel pressure was miles apart which eifher forced it into limp or shut the car down completely.

Is your gauge only checking the low pressure side of the fuel system.