Six is the default setting, but it can be changed. The procedure to increase the number of RBM Workers - on the OPMS server
1) edit the file /etc/default/asm-smartpop-rbtm, and increase the value for number of workers
2) run dpkg-reconfigure asm-smartpop-rbtm to implement the changes
Monitor the OPMS closely after making these changes, as increasing the number of workers will increase resource (memory, CPU, and disk) usage.