In layer blended material Base Material is showing on Top Material's normal

I followed a tutorial for creating an auto landscape material, which can blend between two materials based on the sculpting of the landscape. It has the option to use normal maps for blending between the materials, which adds more detail and realism, but it also causes the Base Material to show up on the Top Material’s normal slopes too, which looks bad.

Does anyone know how I could get rid of the blending on the Top Material’s normal?