These are the results of my experimentation with Thorns.
In the first round of testing I have three armor pieces with 36%, 36% and 32% Thorns. This totals 94% when all three are equipped. My character is lvl 30 with stats 18/17/36/10/10/36/17/23, designed to wear full plate and wield a 2h weapon without being encumbered, and handle all Str and Faith gear at the current level cap. The damage of your equipped weapon seems to have no effect on Thorns, as expected.
At 94% thorns against the training dummy I received 3 damage and reflected 33 damage. Blocking mitigated the damage received but not the damage reflected.
At 36% thorns, with only one armor piece equipped, I took 4 damage and reflected 11 or 12. This suggests that at 100% thorns, I would deal 35 reflected damage, no matter how much damage I took. This also approximately aligns with your value of 316% Thorns dealing 101 reflected damage to the dummy. (Training dummy footage not shown)
I saw the same reflected damage values against all other enemy types I tested, regardless of whether they dealt 34 damage or only 10 to me. Variations appear to be related to the enemy’s defenses. For instance, the enemy who deals fire damage in the following video caused thorns to reflect fire damage, dealing 27 instead of 33. This is likely due to the enemy having some fire resistance (needs verification)
Against enemies who deal slightly larger damage, these results remain consistent.
Certain enemies within the crucible are dealing even more damage to me, but receive the same reflected damage(Not shown, enemies were the armored enemies). Meanwhile other enemies deal more or less damage to themselves, depending on the type of enemy and the type of damage. Again, I believe this is due to their defense values. This ranged enemy dealt more physical damage to itself, while this plagued enemy dealt less plague damage to itself.
Still, in all cases, the thorns damage seems directly linked to the xx% Thorns value, and has no relationship to the amount of damage dealt. Only to the damage type and the enemy’s defenses.
It does not seem correct from the player’s perspective for the reflected damage to be completely independent of the damage of the reflected attack. Frankly, it seems off from a balance perspective to have Thorns damage not scale with anything as the general power level increases.
If the only way to increase reflected damage is to increase the xx% Thorns value, then a lvl 1 character wearing lvl 1 gear with perfect enchantments would deal as much damage as a lvl 30 character with lvl 15 gear and perfect enchantments. Similarly, that lvl 1 character would do the same damage to a danger lvl 25 enemy as the lvl 30 character with their Thorns. This seems unintentional.
Further testing is required to see if levels or stats play into this at all.