I'm 110km from Scafell Pike, the tallest mountain in England. It has a height of slightly more than 900m. This means it's angular diameter from where I am is 0.45°, which is easily visible (it's abut half the size of a full moon).
I can't see Scafell Pike, even when I climb to the highest point around. It can't be a perspective effect (0.45° is easily big enough to see), and it can't be atmospheric degradation (according to FE proponents, when the moon is near the horizon you are looking through 1000's km of atmosphere and you can still see it fine), and it can't be refraction (Snell's law predicts it would be more visible, not less).
So, if the Earth is flat, why can I not see Scafell Pike?