Incoming pressure has nothing to do with the gauge. The gauge registers internal water pressure via the water pump/impeller. That is where your pressure reading comes from. the pickup and associated tubes only supply water, the impeller produces the pressure. As a matter of fact it is not recommended to put too much pressure through the flush port (garden hose connection) and to only let engine idle. On the muffs you will notice the pressure increase with the rpms....point being, don't confuse delivery pressure with engine pressure, they are not the same.
TOXIC