Reflect Damage Skills (Not Monster)

Can someone explain how damage reflection works?

In other words: if a monster would normally hit for 100 and I have 20% damage reflect, which of these cases is true?

• monster takes 20, I take 100, then the 100 is reduced based upon stats
• monster takes 20, I take 80, then the 80 is reduced based upon stats
• 100 is reduced by stats results in x, I take x damage, monster takes .2(x) damage
• 100 is reduced by stats results in x, I take .8(x) damage, monster takes .2(x) damage

None of the above. Monsters have their own stats (armor in particular). You take 100 base damage, reduced by your own stats. The monster takes 20 base damage, reduced by their stats.