If you increase the valve pressure (turn in the screw), you increase the valve's resistance to opening at lower vacuum levels, meaning part throttle or at idle but you also increase the occurrence of compressor surge, which is what a BOV is there to prevent in the first place.
It would appear that the Christmas holidays don’t do much to slow things down at Subaru’s performance division, STI. On the very same day that they unveiled the WRX...