Why is there a need to upgrade to an adjustable FPR, when running a high flow fuel pump?

I assumed that the stock FPR would regulate the flow such that, even when sending it more fuel via a pump upgrade, it would send the appropriate flow (proportionate to the air as determined by the ECU) to the engine, and the rest back in the return.

Is this not the way it works?

Or is the stock FPR more "tuned" to our stock fuel pumps, so sending more fuel to it, via a pump upgrade, will result in the FPR sending more fuel to the engine (and running rich)?

 

For those interested, I finally got through to Nissan and got an answer from them.

Our FPR is "tuned" to our stock fuel pump-letting an appropriate % of total fuel volume through (via pressure on the diaphram). Thus, if you upgrade the pump, it will still allow the same % through, which will be more fuel volume-wise from the larger pump.

So, the adjustable FPR is definitley needed to not run rich with an upgraded fuel pump.