Normal woes on underside of model?

I have a … fishy problem I can’t seem to figure out. The underside of my model is always “flat”. Though I can see the normals from an angle, the further towards a view straight from below, the normals “flatten” from view making the object appear as if it has no normal map on it. If I rotate the mesh in the 3D program and reexport it, the issue then appears on what is now the bottom. I can see this happen on the default shapes I view my material on as well, but I can’t seem to figure out why.

Even if I make a brand new material and use any of my normal maps I get this behavior. I’ve tried flipping the G channel, made sure sRGB is off, and everything else I can seem to find. It’s probably something I’ve done. Which ever side of the model is down, even if it’s at an angle, is flat.

Try multiplying your normal map by a TwoSidedSign node.