The pressure displayed at the group head is more a reflection of the grind's coarseness than it is the control's position. However, they interact to some degree, especially at the extremes of the control's setting.

adcampo wrote: Closed
1/4 turn - 4.1gm per second
1/2 turn - 5.75 gm per second
3/4 turn - 10gm per second
Full - 11.25gm per second
<snip>

Something seems off to me here. I believe that most of us have reported that normal water debit happens around 1.25 to 1.5 turns.
Mine is as follows:
Off = none
1/4 = 1.2
1/2 = 4.2
3/4 = 5.7
1 = 7.8
1.25 = 8.4
1.5 = 9.7
1.75 = 23 < this is not a typo

Okay! That cinches it. As already suggested, your control is not closing. Here's how to fix it, assuming it isn't defective. Loosen the knob, which releases the collar from the spline. Turn the control down all the way closed. Be sure not to turn it down really hard, but you should feel a spot where the needle bottoms into the valve's seat, and it does not want to turn down any farther. Tighten the knob/setscrew. Fire up the machine and rerun your water debit test.

If this does not work, then note that some users have reported a 'gritty' action. If this is the case, perhaps your control is fetching up on a rough bit before it actually closes. Mine was like that. I fixed it by running it fully open and closed a few times with the knob loose. This is easier to do if removed from the machine, which gets the springs out of the way. Eventually, the action became smoother, and the needle went further into the seat in a proper closed position.