Need configuration for queue size w/ ParallelExecutor; as is, limited to pool core size threads, rather than pool max size

ParallelExecutor service is bound to the number of executor threads specified by THREAD_POOL_CORE_SIZE rather than THREAD_POOL_MAX_SIZE, which means by default only three parallel tasks are executed at once rather than the maximum of 20. This is unexpected behaviour for someone not familiar with the ThreadPoolExecutor design, which is not intuitive. The documentation of ParallelExecutor is very misleading and should be expanded to explain this correctly.

This blog post I found explains it clearly:
http://www.bigsoft.co.uk/blog/index.php/2009/11/27/rules-of-a-threadpoolexecutor-pool-size