Shabdbhedi Express: गति इसकी शब्दों को भेदती है, पूरब को पूर्वांचल से जोड़ती है - Dr. Abhishek Rai

RAC seats are predefined and if you do not have an upper berth (or a side lower against the same cubical), it is impossible to have together. If you have such a confrimed seat, it is quite possible subject to number of 2AC coaches in the train.
In fact, a good contribution here comes from the charting clerk.
I give you two extreme examples.
(1)...
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In Avantika, a single ticket for 2 passengers was as follows:
1st Passenger - Confirmed in S-10
2nd Passenger - RAC1
You would wonder that on charting the RAC 1 was assigned with a berth in S-1, while in S-10 also, a number of single passengers was confirmed (it was a clear carelessness of the Charting clerk)
(2)
You would find somewhere in some blogs here only which I had appreciated.
A group of 6 (or 5) passengers was waitlisted.
In charting, 4 (or 3) got confirmed and 2 were under RAC.
The seats provide to them were 33, 34 35 (and perhaps 36) to confirmed passengers in 39 + 39 in the same coach to the RAC passengers.