Some Target Dummies I do extra damage on?

Its always been a thing that if I use certain dummies I will show on details 1-2k extra dps. Last patch Heros Rest was my go to dummy. It had no other dummies too close for aoe stuff in my rotation. Now I come back to Wow retail and Heros Rest is doing it. Any idea?

If the dummy is lower level, it might have less armor. That’s the only thing I can think of.