The problem probably stems from the fact some of the flights are wrongly listed as being flown on 773 equipment, instead of the correct 77W, as mentioned in this thread.

The confusion is compounded by TG internally calling the 773 77R, and the 77W 77J.

While the 773 has no F cabin, I wouldn't be surprised the original contact got around the issue by referring to the 2nd row middle pair as 2E/F when listed as 773.

BTW the middle pair on the 77W is definitely D/G, and you need not worry about finding a 773 on this route, as it does not have the range for BKK-CDG.