How is the loot drop chance working?

Hello,
I am trying to understand what kind of loot is affected by what exactly.
I am unable to find the comprehensive explanation in one place, so please help me to gather it in here.

So far I know:

Loot type:
1. Currency
2. Regular Item (from normal to unique)
3. Boss drop (Boss-exclusive loot table)

Loot modifiers layer:
1. Character bonuses (items, buffs, etc.)
2. Area mods (waystone, tablet, temple, Atlas tree, etc.)

Loot modifier type:
1. Monster Kill Rarity
2. Monster Kill Quantity
3. Chest Rarity
4. Chest Quantity
5. Party bonus (quantity only?)

Currency is affected by any Rarity/Qty applicable to the given loot type (Chest or Kill), same for Regular Items.

Questions:
- Is Rarity on the character added to the Area Rarity? Or is it multiplied by it?
- Is there a way to modify Boss-exclusive drops? If so, how? (afaik cannot be mod and party bonus doesn't work)
- Is it true, that Party bonus affects only Currency and Regular items drop Quantity?

Solved:
- Is Atziri Loot affected by Rarity - Only by Chest loot Rarity, as the loot comes from Chest at the end.