I usually do the 8man Peisteskin maps with 3 people and our chocobros. Everytime I've gotten a rare mat(chinchilla skin/lense/whatever else) and sometimes also 8x philo mats that are bundled into 1 roll for 1 person. Usually get a boatload of shards and other lesser crafting mats that are auto-distributed without rolls.

I did the 8man maps a few times with a full group of 8. We got no rare mats, no philo mats, and very minimal amount of other auto-dist loot. One of the maps was the same as one I did earlier in the day with my 3man group.

Conclusion: RNG gonna RNG most likely.