That was my understanding as well until we were given a table on Deck 3 on QM2 for fixed dining. We had requested a table of 6 and were given a table for 2.
This wasn't a last minute booking and there were a number of tables further back in our section who were also on fixed dining. We were the only ones next to open dining.
The only alternative offered was a move to early sitting.
We declined the offer.