Even this size don't help to increase instances count:
<strict-max-pool name="mdb-strict-max-pool" max-pool-size="1000000" instance-acquisition-timeout="2" instance-acquisition-timeout-unit="MINUTES"/>
Also being discussed here https://developer.jboss.org/thread/261001. As Justin noted in that thread, it's combination of the pool size the and maxSession @ActivationConfigProperty on the MDB. If it still isn't working, please provide more details in that other thread including the exact configurations you are using and also add some details on how you are checking the number of instances.