IMO, there would be no fixed pattern for this RSA, since all rakes shares the same composition, whichever rake is available in JBP CDO they are using it to run the required train on time.
In winters Shridham uses 1 extra rake to make 12192 depart RT from JBP even if 12191 arrives with huge delay, maybe to overcome that or to maintain punctuality of specials from JBP this RSA was done.