Animator ControllerのLayerは上から順に適用される

https://gyazo.com/9dccaba7805f22cd1795373bba777099

公式ドキュメントだとこの辺りから読み取れる

Select Override to use the animation on this layer, replacing the animation on previous layers.

Select Additive to add the animation on this layer on top of the animation from previous layers.

For additive blending to be successful, the animation on the additive layer must contain the same properties as the previous layers.

この書き方だとどっちがpreviousなのかわかんない