The solution: Select the SunSky object and under the list of its components (In the “Details” tab), select the “DirectionalLight” component. Under the “Light” category, change the source angle to something above 1 (I have mine set to 1.25). This will make your sun appear larger (but not necessarily brighter). If you set it to 1, you might still notice a small amount of flickering, so the higher you set it, the less noticeable the flickering is.