A previous statistical analysis of the geosynchronous particle environment by Korth et al. [1999> showed that the particle fluxes are well organized by local time and the geomagnetic activity as measured by the Kp index. Regions of high and low fluxes at geosynchronous orbit are separated from each other by distinct boundaries, approximately matching the Alfv¿n boundary crossings of the geosynchronous satellites calculated analytically from a Volland-Stern electric potential and a dipole magnetic field. Expanding the analysis technique from the previous work to arbitrary, numerical electric and magnetic field models, we reevaluate the Alfv¿n boundary crossings using several available global electric potential models and considering external magnetic field contributions. The more sophisticated numerical models do not do a better job of explaining the observed average access of plasma sheet material to the geosynchronous region than does the simple analytical model. ¿ 2001 American Geophysical Union