Archer %/s (KMS Unlimited and GMS Tempest)

The 50% PDR makes my PDR during the attack 90% instead of 80%.

120 * 0.9 = 108 || 120-108 = 12%
120 * 0.8 = 96 || 120-96 = 24%

So the impact is an extra 12%.
Normally I would do 76% of my DMG, now 88%.
12% is quite some but it can not account for 5.5M DMG on a 18M~ total I believe

Might it be you're missing some defense ignore in your calculations?