@danpe,
What joystick are you using for your throttle channel?
Is your ESC doing the mixing or is the APM doing the mixing?
I use the elevator joystick for the throttle input to my mixing ESC and have limited the elevation channel reverse pwm value to 1.0ms. In my case 1.5ms is neutral, 1.0ms is full reverse, and 2.0ms is full forward.
Regards,
TCIII Developer