Let me clarify one of your observations. By jumping the cold start valve you are allowing fuel into the manifold no matter what the pressure. Your system needs at leat 50psi just to open an injector.
If jumping 30 to 87 doesn't cause the fuel pump to reach at least that pressure the engine won't run. By allowing 20psi pressure through the coldstart the engine will fire, probably not run. Without a gauge its tough because you can pump the tank through the system at 45psi and it will never run (unless you jump the cold start).
As a Floridian (transplanted) I never look to the cold start. Cars don't see cold start for at least 2/3 of the year here. Cold start is usually under 59deg F. It IS NOT a part of starting the car above 59 deg F.
Bosch Master, ASE Master, L1
33 years MB technician