The two person on the FD does not require the both be "seated"
I don’t understand the misconception with the existing USA rule (plus RyanAir and others and which is now being adopted by more as a result of the GW crash).
I just read a post that “cabin crew member …is now mandated to sit next to the pilot when he is on his own.” It does no such thing! It requires that there be two on the Fight Deck. It does not require they be “seated”.
In fact, I understand that under normal circumstances when a pilot is taking a short relief break, the FA simply stands inside the door until the pilot returns. There would be no point in a FA sitting in the RH or LH seat, only to have to get up to determine if it is the pilot that is returning.
When standing behind him, even a slight female FA has quite an advantage over a seated male pilot attempting to take her out. She can manually open the door and retreat to the main cabin. In the GW case, the other pilot would have been there to battle over control, while the plane was on autopilot.