Thanks for setting out the FP versus injector duty cycle considerations. That was an interesting read. The external AFR option, usually mounted remotely to the fuel rail is also a space hog. Prefer something neat and OEM like the Bosch 4 Bar FPR. Might work for you if your current direction of travel with more injector duty time etc etc doesn't play out
Probably wont work in your application but this site offers a Bosch Regulator housing adapter that is designed for the Bosch FPR. There are probably similar offerings out there.