Great news that a formal setting is recommended. I would think 21-22 on a night flight is just about bearable for both the "hotties" and "coldies".

I rather think this is more something BA need to look at securing in their new 'craft. The 767s and 747s currently surely have huge fluctuation in temp from one spot to the next.
Eg1. My wife's aisle seat on the UD was 3 degrees warmer than my window seat on a couple of readings during a flight last autumn.
Eg2. I got up from 3J on a 767 the other night too warm, to go to the forward loo. The galley area was freezing with the (male) CC shivering.

Such severe temperature fluctuations in close areas need designing out.