Have you looked into refraction? I think thats a very easy thing for globe earthers to answer with. I think the thing that flat earthers would have to explain is, why would the object ever not be visible. Meaning, refraction explains why an object would sometimes be visible around the curve of the earth, for instance southern michigan dunes can sometimes see the tops of buildings in Chicago. What flat earthers would then have to explain is, why the bottoms of the buildings were not visible and why Chicago is not always visible with clear skies.