Fuel Pressure Regulator Not Boost referenced only Vac?

Hey guys, working on a car which had the factory fuel rail with fuel pressure regulator as a part of it, I had a vac hose connected to the Intake so I thought this would mean its "boost referenced" I did indeed drop the pressure under vacuum/idle but I noticed while doing a Run it didnt go any higher then 40psi, even on boost.

I should mention this is a N/A engine from factory and the Turbo has been added.

I thought any regulator with a vac hose attached would be boost/vac referenced but I guess not? Or is something wrong with the setup...

If it is supposed to be like that (for this engine/regulator) is there any problems with it being used on a engine with boost? I understand that with say 10psi boost there would only be 30psi differential pressure but is this just a matter of tuning to suit? Im guessing there would be a point where boost is so high (25psi or something) that there is barely any differential pressure and you loose good atomisation as well as having alot higher duty cycle.

I've never come across a fuel pressure regulator that only worked in vacuum. That doesn't mean it doesn't exist however the other explanation that's quite common is that the fuel pump is struggling to keep up and can't produce enough flow to allow the pressure to increase.

If the differential fuel pressure isn't constant it will effect the shape of your fuel curve but you can tune around this. After all that's how a returnless fuel system operates. The problem is that if the fuel pressure doesn't increase with boost, your differential pressure and hence flow through the injector is decreased. Even if the fuel pump can keep up, this will make it more likely that you'll max out your injectors.