Why does cache work better in overlay2 than aufs?

A follow-up from [this question](https://unix.stackexchange.com/questions/510931/overlay-storage-driver-internals) . After reading Docker Storage drivers from [official doc](https://docs.docker.com/storage/storagedriver/overlayfs-driver/#overlayfs-and-docker-performance) I understood that overlay was faster than aufs because it had only one hard linked image layer. But for overlay2, document says overlay2 supports multiple layers as aufs, but mitigates any performance hit with caching. I couldn't find any reference that was showing how overlay2 is better at caching than aufs, can someone give me advices?