Maybe you should take a read. On that page, it has the following sources:
Monster affixes
Rare monsters can receive an monster prefix that gives the monster damage reflection, there is one prefix that reflects physical damage and another that reflects elemental damage.
Map modifiers
Some Map modifiers give all monsters in that map a damage reflection, either physical or elemental.
I followed the links in that source you gave to find the specific mods. Under the monster mods page, we have the following that can spawn on rare monsters:
| Monster Mod | Level | Effects | Mod Type |
|---|---|---|---|
| Elemental Thorns | 40 | 20% of Elemental Damage taken reflected to Attacker (Hidden) | MonsterAura |
| Physical Thorns | 40 | 10% of Physical Damage taken reflected to Attacker (Hidden) | MonsterAura |
As for map mods, there are different tiers of reflect mods, they're a prefix, and the reflect value depends on the tier.
| Tier Range | Map Level | Name | Effect |
|---|---|---|---|
| Low (1-6) | 68-73 | Punishing | Monsters reflect 13% of Physical Damage |
| Low (1-6) | 68-73 | Mirrored | Monsters reflect 13% of Elemental Damage |
| Mid(7-11) | 74-78 | Punishing | Monsters reflect 15% of Physical Damage |
| Mid(7-11) | 74-78 | Mirrored | Monsters reflect 15% of Elemental Damage |
| High (12-15) | 79-82 | Punishing | Monsters reflect 18% of Physical Damage |
| High (12-15) | 79-82 | Mirrored | Monsters reflect 18% of Elemental Damage |
Both of these are added together, giving a maximum of 28% reflect for physical damage, and 38% reflect for elemental damage on rare mobs, and a maximum of 18% reflect on white/magic mobs. However, I did make a mistake.
Damage reflection mods on rare monsters are no longer auras. There are now two new monster mods that reflect physical and elemental damage respectively. They have new effects that are much more visible. A Bloodlines mod has been added for pack-based reflection on magic monsters.
Source: https://www.pathofexile.com/forum/view-thread/1304441
This is the change you're referring to, right? Yeah, the reflect monster mod was an aura at one point. It's not anymore, but the map mod remains global, obviously. I did multiple calculations based on the various values of elemental reflect you're likely to encounter throughout the thread here, assuming the most likely scenarios. The calculation I did above was is still true for the most likely scenario, against a rare monster with full resists in a reflect map. Do I have to compile the others for you, or is that satisfactory?
Either way, I'll make an edit to the aura remark. Yeesh.