Can not adjust PWM min for ESC control

Hi, I am developing a Convergence tilt rotor winged aircraft, using Qgroundcontrol/PX4 with a Pixfalcon flight controller. Only two of my motors are rotating when the vehicle is armed. The third requires more throttle to startup. I tried adjusting the PWM min value for the motor without effect. Even reversing the motor using PWM reverse does not work. But reversing my motor rotation servo using PWM does work as it should. I am using Emax 30 A Simon ESCs. Does any body know how to adjust the rotation speed of the motor at minimum throttle?