Originally Posted by fraser9764

Think about it, if the inlet pressure rises by 1 bar, and the fuel pressure doesn't rise, or rises say 0.5 bar, then the differential pressure between the fuel and inlet has changed so the flow rate has changed, also affecting spray pattern etc.
Yes in theory it is possible to map around this so long as the injectors have enough spare capacity, and you are only running low boost, but it is not good practice, do it correctly and buy a focus rs regulator.