Can you get tier 5 loot in master playlist activities after 450?

I want to farm a tier 5 mercury-a now that I am over 450. Today it is in the Master quickplay playlist, Is it even possible for tier 5 loot to drop from lower level playlist activities, if you are above the recommended power level or does it literally just depend on score?

If I am understanding it correctly getting an A+ score on any activity will give you a tier 5 drop after 450. Then at 500 you just need A or is it B+ after 500? so confusing!