How much damage do "Reflect Damage" creatures reflect?

Does anyone know how reflect damage actually works? Is it a set amount per difficulty? A set percentage? Some combination of the two? Can life steal overcome the reflect damage enough that on average no life is lost or do the two stack in such a way the the reflected damage hits before the time-delayed life steal kicks in and it's still easy to kill yourself?

From my experience it is approximately 5%. This was in Nightmare where some spell I was using on my wizard was doing about 700-odd damage and the ticks I was taking were in the high 30's.

From some of these shots:

• 104/1925? = 5.40%?
• 97/1838 = 5.28%
• 109/2070 = 5.27%
• 109/2073 = 5.26%

35.08% reduction from armor, 23.49% from arcane resist...

5.28% / ((1 - (35.08%)) * (1 - (23.49%))) = 10.63% this seems strange...

At that low amount, you're not in danger of wild swings up and down if you stack lifesteal. That, or passive health regeneration could keep up with what you lose.

According to the wiki:

Thorns / Reflect Damage

Monsters imbued with the Thorns trait, when hit with a melee attack, return 20% of the damage dealt to them to the attacker.

Min. Monster Level: 26.

Available to: Rare, Champion (NOT minion).

Damage Type: Standard.

Additional Resistances: None.

Source: Diablo Wiki