You can’t do anything about it and if you test anything on the dummy, if you deal more damage with a specific setup(like changing items or passive points), you will also deal more damage against monsters, regardless of how much DR they have.
I was reading the GGG about Armor and some other posts about how armor shreds work for taking more or less damages after armor being a nagetive number few hrs ago, confused for a while but I think I figured it out