Dungeon Drop Rates?

Wandering Woods seems like the ideal place to farm Spellshards, since only them and Venomstone can drop there, but on Theodora’s part I deployed a battalion there and got 20/20 Venomstones a couple times, while seemingly had more luck at Giant’s Print Fort even though Lunar Stones are hogging space in the same rarity tier there. This seemingly implies that rare materials drop more frequently at higher level dungeons, but I’d like to hear if this has been true for other people to try to figure out the best Spellshard/Umbral Steel farming spots.