FMU arent really precise on fuel delivery vs rpm. You figure it adds more fuel per lbs of boost, if its already making almost all the boost by mid rpm range, its probably dumping too fuel as that level, but leveling out at the top end.

We had a car at the shop we built. It was a 331 with trickflow r intake, brodix street r heads, solid roller cam, vortech a trim kit. We honestly just unhooked the vacum line for the fmu, adjusted the fuel pressure regulator. It ran decent with 42# injectors, still good have used a tune though.