Monitor per object (node/pool member)

In this case the port is determined by the monitor, not by the node. Hence you can assign it to a node.

Compare the following monitors:

tcp - has no port assigned, cannot be assigned to a node

tcp_777 - has a port assigned, can be assigned to a node

https - has no port assigned, cannot be assigned to a node

https_443 - has a port assigned, can be assigned to a node