How does armour damage reduction interact with other life types in Overwatch? [duplicate]

As we know (for example this question What's the difference between life, health, armour and shield?), armour in Overwatch has a damage reduction property.

Reduces incoming damage by 5 if the hit was 10 damage or more. If the damage is less than 10 then it is halved.

My question is the specific mechanics of how this interacts with other health types. Knowing this may not actually effect the outcome of any situation in game, but I'm curious as to how the system functions. Questions I have are:

Does damage reduction apply if you have a shield or overshield which would absorb all of the damage from a shot?

Example: Armour: 50, Shield 30. I get hit for 15. Do I take:

1. 15 damage to my shield - no damage reduction.
2. 15-5 = 10 damage to my shield - full damage reduction.

I assume 1. will be the case.

Does damage reduction apply to all, some or none of a shot when you have a shield / overshield which would block some of the incoming damage?

Example: Armour: 50, Shield 5. I get hit for 10. Do I:

1. Take 5 points to the shield, then a full 5 to armour (no damage reduction).
2. Take 5 points to the shield, then 5/2 = 2.5 points to armour (damage reduction on the "remaining" damage)
3. Take 10-5 = 5 points to the shield (damage reduction on the whole incoming damage).

I'd assume it'd be 2.

Does damage reduction still apply if you don't have sufficient armour to absorb the entire shot?

Example: Armour: 5, get hit for 15. Do you:

1. Take 15-5 = 10 total damage (5 to armour, 5 to life) - full damage reduction.
2. Take 15 damage (5 to armour, 10 to life) - no damage reduction?

I would assume 1.