I am nowhere near your level but I did see a vid from esotetickk with some tips here: [url]https://youtu.be/IL5yKwq5HdY?feature=shared[/url] I also saw another vid (but can't find it) that said the reward tier of the activity deffo didn't matter i.e. the prime engrams had the base 5% chance of dropping regardless of activity reward tier.