Please run physbone components for a few seconds before impostor generation to allow hair, pistons, skirts, and especially tails to fall into rest pose. Many avatars with tails have the tail modeled sticking straight out for better deformation when bending, but this also causes the tail to be sticking straight out in the impostor.

Add a side note honestly I think all components including physbones and constraints should be run during impostor generation. If you're have this system which takes a snapshot of an avatar, thus negating all performance cost, it seems silly to capture said avatar without it fully running.