/3/ - 3DCG

I'm trying to break up some obvious patterning on a normal map in Substance Painter.
I had figured I could just make a few duplicates of the original, change the seed values, then blend them in with a noise mask (also at different seeds), but for some reason, instead of straight replacing what is below it, it just adds them together making the normal map stronger. I've tried changing the blending modes in the normal channel (including each of the different types of normals blending in there), but nothing really works.
I'm not really sure what I'm doing wrong, because in my head it made sense that it would work.
Is there something I'm missing (like a filter that breaks up patterns) or something special about layering normal maps to replace what's underneath?

Pic related. Hopefully it shows up well.
Top is original without layering. I circled a pretty obvious shape that repeats to show the tiling.
Bottom is with another map layered on top to break it up. It breaks it up, but as you can see the normal map is stronger. I thought it wouldn't make much of a difference, but it definitely shows up in material view.