My question regarding this quote is: How do you think it's possible to see 300 miles away when your magic sphere should be hiding the image with 60,000 feet of curved water?

By looking from one high point to another high point.

From up on Mt. Hood when I was not quite at the peak but at approximately 10,000 feet I could see to the Three Sisters (about a hundred miles away) which are also about 10,000 feet. In between, the land was much lower.