Out_scale factor usage in multirotor mixer especially when the gravity center is partial

Hello,everyone. I have a question about multirotor mixer.
outputs[i] = (roll * _rotors[i].roll_scale +
pitch * _rotors[i].pitch_scale) * roll_pitch_scale +
yaw * _rotors[i].yaw_scale +
thrust + boost;
The above is the final mixer of multirotor.Why the out_scale is not present?That will lead to reverse when the gravity center of the multirotor is partial.Is there any explanation? Thanks.

Same question. BTW, is there a reference on the assumptions made in the implementation of mixer?