GBuffer Normal Precision

Hello, I have been trying to make changes to the rendering system of UE4. I have removed all post processing and i noticed that the specular at low roughness were very scaly. I looked though the source and saw that the format used for normal were rgb10 with unused a2, which seems to be too low for the smooth speculars before I made any changes. So I am wondering how are the normals modified so that the specular was smooth?