what i think is that you see a difference in it if you reach specific goals, lets say (i'm totally guessing numbers just to explain what i think) it increases the damage landed by a critical by 1% every 1000 units of injury stocked, then you need to reach 2000 to see a difference in comparison with 1000 (so, lets say you are at 1600 if you add 240 you reach 1840 that's still under 2000 so you don't see any difference, but if you add another 160 you see it).