Does anyone know: If you are inside an enemy's guardian shield radius and you use a ranged attack, does it still have 2 reduced damage?

Allied units under a Guardian Shield still take reduced ranged damage regardless of where the enemy units are firing from. This means that one Marine could stand within an opponent's Guardian Shield, and another Marine could be standing outside of the shield, and they would be doing equal damage to any units protected by the shield.

---

Q u o t e:

No.

Any unit affected by the Guardian Shield buff gets a -2 damage taken at the very end of the damage recieved calculations.

---

This is correct. The Guardian Shield buff does not stack.