The feeling I get when looking into middle ages life is this. The Church supported Ptolomy's geocentrism, that is the Earth was a perfect Sphere at the center of 7 more perfect spheres. The idea of the perfect sphere was part of God's perfection. Anyone who studied at university would know this. Most people did not study at university, however. If a commoner wondered what the shape of the Earth was, and they were unsatisfied with "my family's field is flat, but the mountains over there are pointy," they would go to the church and see paintings of people holding globes. If the priest knew, he would say "my son, the earth is a perfect sphere as The Lord has made it" or words to that effect.

This is based on reading a bunch of secondary sources on the middle ages and seeing photographs of stained glass windows, paintings of kings holding globes, and others reproductions of primary sources.