The problem is when you think a ship sails over the horizon, you can increase zoom and it returns to view. I've done this myself.

Go to the beach and bring binoculars and a telescope. You can visually see it anymore, use the binoculars and like magic its back in full view. When it sails over the horizon again, use the telescope and again it will return to full view.

The problem seems to be the optics used and not any actual curve.