There’s other stuff in the material editor, and texture editor, too…that is for working with normals (imported and in-engine created content). One option to use is in Project Settings > Rendering > GBuffer Format, select “High Precision Normals”. Then open the mesh in the mesh editor in UE, expand Build Settings, and enable “Use High Precision Tangent Basis” and “Use Full Precision Tangent Basis”. Those are specifically for enhancing / fixing normals and getting better quality reflections. I don’t know 100% that it’d work for the leaf’s case, but it’s worth a try.