Navigation Mesh Generation Settings aren't doing anything

I recently went into my projects settings, and under Engine>Navigation Mesh>Generation, I changed the Tile Size UU from 800 to 1200. This indeed made the tiles bigger when the mesh generated, but when I changed the value back to 800, the generated tiles remained the same size! Does anyone know what is going on here and how I can get the tiles to go back to their original size? Thanks!