A new method is reported for characterizing focused ion probe current distributions based on the comparison between damage simulations and transmission electron microscopy observations. Several focused-ion beam operation conditions were modeled, such as low-to-high source emission currents and variable beam acceptances. At low current and small acceptance, the ion spot exhibits a nearly Gaussian profile, otherwise larger tails are evidenced which can be modeled either by Pearson or "bi-Gaussian" distributions. The sensitivity of the procedure to the tail extension is highlighted.