Airbond,
In Qantas: the Captain logs PIC, for the entire flight. Everyone else logs co-pilot, regardless of seating. Except the F/O doing ICUS thing already discussed.
We generally do not have "relief / cruise Captains", however if more than one Captain carried the additional Captains log co-pilot only. Only the Captain designated the Captain in command logs PIC.
Not my idea, I just do as paid.
