I makes no sense to have only one instance that holds the JCA-EIS connection pool, I will give you examples.
I asume that you use cluster for failover and loadbalancing.
- each access on a node force a 'remote' access to lookup and use the connection
it is not a big difference (except the network traffic and latency) whether the nodes are on same/different systems
- if loadbalanced the sum of connection is the same if you use it in parallel, nevertheless it is one node with 40 or even 4 with 10
- If the node with the connection pool crash your application is down
- distributed XA transactions (I suppose that you are using the EIS system together with database access) are not supported by default
which you have to use in that case
So for me the best cluster configuration is to configure all nodes in the same way (number of connections, JVM params, deployed apps ...)