Can the reflected damage be blocked or mitigated in any way?
Does dr% help against thorns?
DR%, pdr, mdr overflow, other forms of dmg reductions such as ES, bone armor, pvp penalty all reduce the dmg taken by your enemy, thus reducing the returned dmg you take. The % returned dmg is based on the final dmg taken.
Then the returned dmg is also reduced by the same things listed above that YOU have.
So for example, in pvp, the returned dmg is modified twice by the 0.17 factor