There is a chance I'm incorrect, but I believe the fan can be controlled directly by adjusting the numeric value in the file

/sys/devices/ocp.3/pwm_test_P9_31.12/duty

cat that. the formula seems to be 12000 + (%% * 200)

for max fan at 100%

echo 32000 > /sys/devices/ocp.3/pwm_test_P9_31.12/duty

for fans at 50%

echo 22000 > /sys/devices/ocp.3/pwm_test_P9_31.12/duty

personally, I would not go less than this. but if you must, feel free to plug in whatever value you want and have at it. watch your asic screen though, if you start getting too many 119C (they show up as red), then they will downclock and you will lose hashing power.