Question: Drop rate mechanics for Elite Chests & Watch Crates

[gundamsone]

With every new addition of an Arcane/Mythic item added to the possible loot list, are our chances at looting these increased?
I have a few scenarios below of how the loot system might work in this game.

Scenario 1
So lets say the loot rates are the following for the items below:
Hammerjaw 0.1%
Mythic Rogue Helm 0.3%
Mythic Warrior Helm 0.4%
Mythic Mage Helm 0.5%
Are the chances of looting any one of the items above increased to 1.3% (or the sum of all the drop rate %'s)

Scenario 2
The drop rate set to a single value for example lets say 0.2%.
If one is lucky enough to roll on this drop rate, then one of the items from the possible loot list is randomly selected and given to the player.

Scenario 3
The drop rate set to a single value again for example lets say 0.2%.
If one hits rolls on this drop rate, then the item given to the player is based on another % rate.
For example there's 1/10 chance to loot the hammerjaw, 2/10 for the rogue helm, 3/10 for the war helm, 4/10 for the mage helm.

Which scenario do you guys think is the most likely one implemented (or if another one) & it would help alot if a Dev can clarify on this for everyone.
*not asking for the specific %'s but how the drops work*