I think a potential sourse of confusion here is exactly what we mean by "sideslip" under aysemetric thrust.
Traditionally sideslip was indicated by a ball in a curved tube which in straight line flight indicates the direction of gravity. This we might call "indicated sideslip"
True sideslip is the direction of the airflow relative to the fuselage centerline. It could theoretically be measured by a vane or, in an aeroplane with a one piece windscreen, by a piece of string in the center of the windscreen like glider pilots use.
Under symetric thrust, indicated sidslip is the same as true sideslip.
Under aysemetric thust however true and indicated sideslip are not the same.
Any true sideslip is a source of drag due to the fuselage being not aligned with the airflow. For min drag therefore we want to find the zero true sideslip condition. At zero true sideslip there will be an indicated sideslip towords the live engine.
I suspect that the little rectangle under the bank pointer shows indicated sideslip, not true sideslip.