Wow...so simple made so difficult!
Operating crew need 3 hours rest or more to extend fdp. If flight time is sufficient then the relief crew can also have 3, if insufficient priority is given to operating crews.
It seems its only the newbies who haven't operated this before who want to read this differently as it effects them as the relief crew!
No 3 hours rest for "A" crew, no extension of FDP!
Not rocket science!