'90s Rover EFI fuel pressure regulator

[en]

HI
I'm slowly learning how these systems work.
I've read of rising rate fuel pressure regulators, but these are the opposite.

'The regulator is a mechanical device controlled by plenum chamber vacuum; it ensures that fuel rail pressure is maintained at a constant pressure difference of 2.5 bar above that of the manifold."

at Wide open throttle, plenum vacuum would decrease? the regulators would maintain a lower fuel rail pressure?
I hate asking basic questions, but i haven't had any luck finding a good source book on how the system works

[BlownMGB-V8]

Manifold pressure increases at WOT. (vacuum decreases to near atmospheric). So the reference signal to the FPR increases, which increases the fuel pressure.

JB