At the time of sunset the sun appears to be at an altitude higher than its actual position. This is because of

Refraction of light

The density of the atmosphere is not even and decreases with increasing altitude. At a result, when sunlight passes through the atmosphere, successive refraction occurs and bends the sunlight towards the ground. If we look towards the Sun, the altitude of the observed Sun's image (i.e. the apparent position of the Sun) will be higher than the actual location of the Sun.