As suspected, the NPAS in the nozzle is very different from that of the regular open bolt design.
Here's a closer look:
The part on the right (the tail) controls the fps. The part on the left (the head) is free floating and held in place by a spring.
At rest, both the head and tail parts "mesh" together allowing gas to flow both toward the front of the nozzle and also to the rear of the nozzle. The gas pressure building at the rear pushes the head forward against the spring until it goes so far as to "seal" the front of the nozzle thus stopping all gas flow to the front of the nozzle. All gas now flows to the rear of the nozzle and into the bolt carrier which moves back past the trigger assembly and disengaging the firing pin, stopping the gas flow.
The more you open the NPAS on the tail part (ie counter clockwise turn), the further forward you push the head in the nozzle. FPS is reduced because it will take less time for the head to seal the front of the nozzle and stop the gas flow towards there. Less gas flow = lower fps.
Now the problem with this design is that it is possible for the head to misalign with the tail as it returns back to rest position. If that happens, the head would be too far forward and your next shot would have significantly lower fps, until it is realigned again.