Position of the pressure relief valve doesn’t make any difference in the reading but the position of the check valve does. If the check valve is near the gauge, you’ll get a false reading as the hose will think it is part of the compression chamber in the motor. In other words, the hose will be an extension of the compression chamber, resulting in a low reading. The check valve must be located at the end of the hose or in the fitting which screws into the head. The motor must also be spun over enough times to allow the pressures in the hose and the compression chamber to equalize to get a true reading.
Check valves at the fitting.
