Communication between leaf nodes

[chgz]

I tested the deployment model above.
Found that:
nc2 subscribes to subject: foo, nc1 publishes foo's message, nc3 can receive it but nc2 cannot.
Can anyone tell me how leaf nodes communicate with each other, or are they not allowed to communicate?
I looked for the document and did not find any relevant description.

[chgz]

I used the same server_name for leaf node 1 and leaf node 2.
Change it to a different one so they can communicate.

However, I have read relevant documents and it is not clear that server_name will affect the spread of traffic