Yes you are right. FC should always be trying to drive ESCs to level the quad. In a case like mine in which the quad is already levelled, pwm outputs to ESCs should be single value. In a propeller mounted case, my quad leans on a direction when I throttle up even it is leveled. I am trying to learn what could be the problem of getting this outputs not same for all ESCs when quad levelled.
It works quite meaningfull when I move FC, the servo outputs fluctuates as it should be. Such, when I roll right it drives the right motors more etc. But, in a levelled case there should not be any difference on the speed of the motors. Thats my problem.