Not sure what the GP intended, but one possible effect is that increasing the focal length ('zooming in') would change the relative size of two objects (one closer, one further away) depending on their relative distance to the camera (I think the closer object might appear relatively larger).
But if the sun and the horizon are the intended objects, they are both effectively at infinity, from the camera's perspective, so I wouldn't expect focal length to change anything in this case.
Changing focal length of a lens ('zooming in') does not change relative size of two objects, it is a common misconception. What changes relative size of objects are your legs when you move from one spot to another to get roughly the same framing with different focal lengths. If you stand in one spot and zoom or change prime lenses relative object sizes stay the same.
Fair point - I should have tried this with an actual camera. But I suspect my line of reasoning still stands, that the focal length doesn't affect the phenomena being discussed here
That article specifically clarifies that moving the camera is what causes changes to relative sizes, not the focal length. But in the experiment described, the camera doesn’t move a significant difference with respect to the sun, the camera can’t really get anywhere close enough to the sun or the reflection on the horizon to make any difference, certainly not 20%.
