I just did LHR-SIN, originally booked in 14K. During boarding, I noticed that the entire front cabin (16 seats ex-crew seats) filled, but the rear cabin (42 seats) was light. I asked the purser if I could move, and went to 18K. No one in front of me, no one behind me, no one across from me. We ended up with just 13 people in the rear cabin. The full compliment of FAs worked the rear cabin, so the service was really super.

So I don't know if this happens regularly, but if it does and the front cabin is filled first, then you might have a much quieter and relaxing trip in the rear cabin.