He should look like he is about to not be there.
Built for the pose more than the portrait. A character defined by leaving needs a silhouette that already looks mid-departure.
Static poses kill him. Every angle has to feel like it was caught rather than arranged, which means the balance is deliberately wrong in a way that only works from certain sides.
The tail does more compositional work than the figure does. It is the line that ties the pose together from behind.