Reduced Damage + Additional Physical Damage Reduction - Stack?

As the title says, do generic sources of reduced damage (Bloodletting, Silent Steps, etc) stack additively or multiplicatively with additional physical damage reduction. It’s just a tense issue between reduce and reduction, but they are worded differently enough I’m not sure.

additional physical damage reduction stacks with reduction from armour formula -> phys damage mitigation

reduced damage taken comes in next step, after mitigation