I observed that, the px4 gives slightly higher throttle when first arm, then it is true idle throttle afterwards.
When I arm at first (first arm after power cycled), PWM output is around 1200uS.
This is measured by SERVO_OUTPUT_RAW.servo1_raw to 4.
But if I make throttle low couple of seconds, it become 1075.
PWM_DISARMED = 900
PWM_MIN = 1075
PWM_MAX = 1950