I attacked a dummy to test a completely different thing. But then I noticed that I was doing far less damage than expected. From what I read dummies have around 18200-18500 armor?

Attack with cp160 gold weapon, surprise attack tooltip 4666. Actual damage 2968. (no penetration in cp or trait, no debuffs)

If dummies have 18500 armor they should mitigate around 27-28% of my damage. (armor/660). But it actually mitigates 36,4%.
I tried allocating 160 cp to see if the game was counting me as a low level. But mitigation stayed at 36,4%.

Any idea why this is?