Link between ACCY vibration, PWM output and Motor tilt

Although I do not think my issue is not software related, I want to ask the experts about the correlation between ACCY vibration, PWM output and Motor mounting tilt. When optimizing the tilt to achieve a balanced PWM output (drone itself is basically balanced), I see a strong ACCY vibration, while ACCX and ACCZ are quite good.

https://logs.px4.io/plot_app?log=883a7573-0620-48b3-9523-018cf0d0c291

When adjusting the tilt, I can manage to reduce the ACCY nearly to the level of ACCX and ACCY, however the PWM output of motor 3 and 4 (Quadrocopter) are far from PWM output of motor 1 and 2.

Any idea, what could cause this dependency?
Thank you.