Whether the system fuel pressure gets up to 65-72 psi or that the pressure stays there when the key is off?
Are you having driveability/starting issues?
On the returnless fuel system, the fuel pump is the driving force behind system pressure...Remember, in this system design, there is no vacuum line to vary the fuel pressure based on engine load via vacuum...Since there is also no fuel return line, the injectors, fuel filter, and the fuel damper[which is used to smooth out fuel pulsations from the pump] will determine the delivery of fuel to the engine... The regulator is apparently in the system to "vent" excess pressure back to the tank while maintaining system pressure in case the system pressure goes higher than designed...
The pump and the injectors will also act to maintain fuel system pressure when the engine is off...My understanding is that Ford went to the returnless system and subsequent higher fuel pressure to fight iisues with heat soak causing vaporizing in the lower pressured fuel lines and difficult hot starting...
The pump has a typical check valve in the output port to stop backflow of fuel back into the tank and the injectors obviously have solenoids to turn on and turn off the fuel flow and keep the fuel supply at the ready on demand from the PCM...
Typical leakdown issues would be either a defective injector bleeding through the solenoid and/or a defective pump check valve in the pump itself...In the years that I have worked with the Ford returnless systems in converted Rangers and other vehicles using the Ford system I have only had to replace a fuel pressure regulator and that was when rust from the fuel tank caused the bladder to stick open and bypass the majority of the fuel volume back to the tank instead of supplying the fuel rail...