Excitons in van der Waals monolayer materials have attracted broad interest due to their high binding energies, strong light-matter interaction, and intriguing spin-valley physics, motivating the question of their appropriate description. Using magneto-optical spectroscopy, the authors explore the spatial extent of the excitons in WS monolayers, focusing on the properties of the excited states, including valley Zeeman and diamagnetic effects. The results further confirm the Wannier-Mott nature of the excitons in semiconducting monolayer materials and the assignment of the optical resonances. They provide additional support for the applicability of the effective mass models, based on the thin-film Coulomb potential.