When the angle between the incident ray and the mirror is increased, the angle of reflection decreases. Because of the glancing angle of incidence, this is the case. The angle created by the incident ray and the mirror is known as the glancing angle of incidence. In addition, the angle of incidence and the glancing angle of incidence add up to 90 degrees. As a result, as the glancing angle increases, the incidence angle decreases. Angle of incidence equals angle of reflection, as we all know. As a result, the angle of reflection is reduced.