I have Asrock 970 extreme3 + nanoxia fan PWM (500-1500rpm)
I connect to MB PWM (4pin) and i only can change the rpm to 1120 from 1500rpm.
I setup level 1 and i can not setup under 1100 rpm.

Why?
M4H02873 - YouTube

other fan like cooler master 3 pin i can control under 1000 rpm