This study suggests that the unavoidable spatial inhomogeneity of intense electromagnetic fields has a drastic effect on the electron-positron pair creation process from the vacuum. We use the example of the Breit-Wheeler process, where the collision of two gamma-ray photons is predicted to create electron-positron pairs, to show that the multi-photon pair creation process cannot be modeled by solutions to the Dirac equation under time-periodic fields that are spatially homogeneous. The neglect of the spatial inhomogeneity leads here to spurious energy spectra and misleading pair creation yields that can be incorrect by up to several orders in magnitude. This finding is surprising as there are many widely cited works where the laser is modeled by a spatially homogeneous alternating electric field.