The number berths opened for RESV at 90 days mark is around 425 ( which means around 78*5 PLUS some other emergency quotas which makes sense that only 6 bogies are awarded full quota of booking for every journey.
But 2274 has 9 SL coaches hence the number of waitlist passengers have chances for confirmation to atleast 2 bogies i.e 156 berths or upto WL156.
And probably if there isn't sufficient WL passengers then SL berths are awarded to RAC passengers thus confirming the RAC's to Confirmed with indivudual berts.