Did long haul flying for 16 years. 4 man crew 15~ hours. Most captains would send an email well ahead of time making it clear who's flying and who is relief. No problem planning rest. Besides, it makes no difference Who gets first or second rest. The takeoff/landing crew can be out of the seat and into rest at top of climb if not earlier depending on airline policy. You got first choice of rest if you're the takeoff/landing crew. Never a problem and who gets to fly PF was always decided based on currency unless limiting conditions such as LVO required the captain to be PF. Some people have very rigid sleep patterns from which they can't deviate and long haul flying is not for them.