Stock vs Aftermarket fuel pressure regulator?

[Bob_n_Cincy]

I thought I had a good understanding of the fuel system.
Since all fuel systems for our Subaru engines are designed to hold a constant 43.5psi of differential pressure.
Why is a tune needed if a pump or regulator in the fuel system is changed?

Sounds to me like your covering up a fuel system problem with a tune.
Bob

PS: I have a OEM jet pump on my return line that has restriction. I could see this causing a problem if I would go to a higher volume pump.