Your problem is you're bringing math into it wrong.

You see, Earth is actually a hypersphere. You can get to Agatha, which itself appears as a normal 3d planet, through tunnels that twist ana to kata. That's why water seems to sometimes flow uphill - that's a sign that a tunnel might be close.

There you go. It's got secret lore, it encourages learning math, and it gives people a hobby where they look for inconsistencies in physics instead of rejecting it. We could even make some interesting discoveries if people are going out trying to find places where physics is weird.

It's basic math, if you want to reduce flat earthers, you have to cancel them out