Can I adjust the output PWM of 2 of the 4 motors in a quadplane (DF log attached)

My quadplane (modified from Bixler 2) constantly pitched forward during testing. After downloading the DF log, C6 and C8 in RC OUT, representing the 2 rear motors have the highest PWM of all the 4 motors. Does this explain the pitching forward ?

During Motor Test in MP, these 2 motors need highest Throttle % to start.

Is there any way to reduce the PWM output of these 2 motors ?

If it always pitches in the same direction, check the motor wiring order. it is incorrect. Or the flight controller mount orientation parameter is incorrect

Motor wiring and mount orientation are both correct. In fact, I solved this problem by re-calibrating the ESCs.
It is confirmed by flight test(no more pitching forward), and RC OUT in Mission Planner shows very close PWM output of all 4 motors
after flight test. Also motor test in Mission Planner reveals much lower Throttle % to start the motors compared to that before re-calibrating the ESCs.