The tendency of the reflectance of a material to depend on the viewing angle is called the Fresnel effect. A material may be more specular from a grazing angle than from a head-on angle.
Note
The Fresnel effect has magnitude at a grazing angle. This water material seen in the preceding screenshot has high specularity and opacity at a grazing angle due to use of the Fresnel effect.
UE4 has a specially built-in capability to account for this. We'll construct a water shader that has view-angle dependence for translucency to give an example of how to use the Fresnel effect realistically.
You need a new shader to which you want to add the Fresnel effect. Preferably, select a material that you want to look a bit different depending on the viewing angle.