Electron transport across the magnetic field in Hall effect thrusters is still an open question. Models have so far assumed 1/B² or 1/B scaling laws for the “anomalous” electron mobility, adjusted to reproduce the integrated performance parameters of the thruster. We show that models based on such mobility laws predict very different ion velocity distribution functions (IVDF) than measured by laser induced fluorescence (LIF). A fixed spatial mobility profile, obtained by analysis of improved LIF measurements, leads to much better model predictions of thruster performance and IVDF than 1/B² or 1/B mobility laws for discharge voltages in the 500–700 V range.