Permeability and form coefficient are the characteristic hydraulic properties of any porous medium. They are determined simultaneously, for known fluid thermo-physical properties by using the Hazen-Dupuit-Darcy model (HDD) to curve-fit the longitudinal global pressure-drop versus average fluid speed data from an isothermal, steady flow, hydraulic experiment across a test section of the porous medium. The and thus measured are global parameters, i.e., valid for the entire porous medium and universal provided the flow throughout the porous medium is of plug flow nature. We report here experimental evidence on the influence of non-plug flow velocity profiles at the inlet, on the simultaneous determination of and of fissure- and rod bundle-type porous inserts. Although variation in is minimal, as much as 12.1% variation in is observed, when going from a fully developed velocity profile to a plug flow profile at the inlet.