Question. Have you ever taken a p-900 and done this yourself? Because if you had you would know this is not possible (although seemingly larger you would still see the sun fractionally against the back drop of the ocean)...What your talking about is conjecture. Your talking about a sun that is above the horizon so by your definition the whole sun should shrink until you can't see it...Not half vanish and half appear.
It has nothing to do with perspective that is a pseudo explanation which is entrenched in confirmation bias. I appreciate that you expose the truth in other subject matter but your simply wrong about this one.