By right in the middle, I mean the way it came from RAW. the screw head/plate is flush with the breech block. I've turned it clockwise so that the velocity increases and the head/plate becomes recessed. I haven't tried it yet, but I'm assuming that I can turn it counter clock wise so that the velocity decreases and the screw head/plate will stick out a bit from the back of the breech block. I'll let you know if this is so.
I didn't do any testing with ES and SD when it was new. Just looked at velocity, so I can't compare. It's still pretty new. Have only had it since December and probably have only put 500 rounds through it. So, don't know if this is enough to break in the regulator.