You can use both approaches, both should work:
1) One Session -> Multiple Processes
2) Multi Sessions -> One process
By Persistence Configurations I mean sessions and processes persistence configurations :)
http://docs.jboss.org/jbpm/v5.0/userguide/ch08.html
http://docs.jboss.org/drools/release/5.2.0.CR1/drools-expert-docs/html_single/index.html#d0e2697
Cheers