How does Shield Up work?

[MagicManICT]

In general, amount of damage dealt has been equal to the percentage of the attack that didn't get blocked. If the attack does 100 damage, and 30% of the attack was blocked by defenses, 70% of the attack got through, and 70 damage is dealt to the target. Armor mitigation and absorption then reduce damage damage dealt to the player. Ideally, when fighting PvE, none of the damage makes it past mitigation.

I've not done an extensive study on this this world, but I haven't seen myself or seen it posted to the forums that this has changed, so apologies if I'm wrong on this.

Note: I'm assuming by "reflection" you mean the armor mitigation, or deflection, amount.