After some testing, I can say that Divine Aegis works thusly:
- If you cast a critical heal on a target, they gain the Divine Aegis effect, which lasts for 12 seconds and absorbs 10/20/30% of the total (not effective!) heal amount. (I was using Flash Heal to test, so I was getting 1.5-2k DAs.)
- If you or another Disc priest casts another critical heal on the same target, the Divine Aegis effect refreshes its duration (back up to 12 seconds), and 10/20/30% of the second critical heal is added to the remaining shield from the first crit heal. For example, I establish a 1.5k DA on the Tank, the Tank takes 1000 damage, and then I cast another crit heal on the Tank for another 2k shielding, which makes the total shielding 3.5k and the remaining shielding 2.5k (since the shield absorbed 1k damage between the first and second crit heal).
- The maximum damage that a single DA can shield is the level of the target * 125. That’s 10k damage for a level 80 tank. If a DA reaches this amount through repeated application, and you cast further crit heals on the target, the DA’s duration will be refreshed but no additional shielding will be added.
- When the DA buff wears off, the next crit heal starts the process over again.
- You can have Divine Aegis going on more than one target at once. Each shield has its own independent shielding total and duration.
I hope that’s helpful!