Here are the findings of some ingame tests with Lucky Charm (done in the basement of the Witch Cabin after teleporting down to the Grotto first times).
Lucky Charm varied from 1 to 8 on both main characters (both had the romantic trait). There are a chest, many crates and barrels, baskets, and some bookcases.
1. Lucky Charm has no influence at all on loot generation, neither in the chest nor in other containers,
if there is no "lucky find" (indicated acoustically and with four-leaf clover animation on PC).
2. A lucky find however changes subsequent loot, perhaps like an additional opened container would do.
3. All lucky finds are identical for Lucky Charm 6, 7 and 8. This is consistent with the loot table
linked in the previous post. For lucky finds, Lucky Charm is capped at 6 (but not for offense rating).
4. Even a simple basket may yield a ruby as lucky find.
5. It does not matter, whether you open a basket down below or above outside the witch cabin.
6. If does not matter, whether a barrel opened is here or on a different map (Hiberheim - Cave Entrance).
7. It does matter however (!), whether a main character or a companion opens a container.
8. A main character and a companion will see the same content, if the chest is opened first (only there).
9. After reset (after 5 hours ingame time or levelup), even the trade windows of Cyseal legionairs
will change your lucky finds and other loot in the Grotto or in Hiberheim.
Lucky Charm can be increased by the romantic trait, crafted rings and belts, and bought or found boots and shields, therefore it is possible, to bring it to 6 without investing any ability points. If the loot table linked above is implemented correctly, the probability for a lucky find in the "precious" category (a pearl, painting or ruby) should be 0.010 with Lucky Charm 4 and 0.008 with Lucky Charm 6.
I don't plan to use combinatoric exploits, but as a measure of precaution, I consider any unopened barrel or crate near a waypoint as a precious resource by now, and do not touch it - like a quest (i.e. Elf-Orc Blood Feud) with reward chest or Evelyn's secret lockbox.
