You have it backwards. The nut-locked allen screw in the center of the RRFPR is used to adjust the "baseline" fuel pressure. The recommended procedure is to disconnect the vacuum line from the RRFPR, letting it reference atmospheric pressure (i.e. neither vacuum or boost), and setting your fuel pressure to where you want to it be when you are transitioning from vacuum to boost. The thumb adjustable screw is used to adjust the rate that the pressure will rise when under boost. If it is screwed all the way in, you are definitely going to be running too much pressure, too much fuel, and possibly could damage the injectors.
No fuel pressure gauge? I'd recommend hooking one up at least temporarily so that you can get things straightened out.
Hope this wasn't a Subaru tuner shop that left you in this condition!