As another data point, and based on two ET bookings in the last couple of months, two Golds booking together are initially auto-placed onto the A and F seats (or A/D ex LCY) sides of the aircraft in the same rows.
I had to go back into MMB to put my wife and myself together again.
We are currently in E/F exit rows for our LHR departures - I will be interested to see whether we get the D seat free to expand into when we actually fly.