that is not an adjustment on top of the FD.
the limitation on the sys
PR is the small openings in the pistons inside.
blocked return is only thing that will give you fuel PUMP pressure after the FD.
even if the sys
PR was working to its full capability you would have SOME sort of drop in pressure but it sounds like have the same pressure before the FD as after.
blow through the return like, you should hear bubbles in the tank
do the fuel FLOW test.
i have two sets of those gauges.
one set reads much higher than the other above about 4 bar. both were new at the same time.