I'm not sure if the the piece side continues to have bearing when the hashes are all in a Merkle tree on uniform 16k blocks.

"Enforcing these encodings also help make it more likely that two people creating a torrent from the same files, end up with the same info-hash and the same torrent."

In the discussion of backwards compatibility, it appears that v1 collections of identical content encoded with different piece sizes will all become the same v2 collection when upgraded.