The phenomenological theory for the anomalous electric double layer (EDL) impedance response (see J. Phys. Chem. C 118, 2014, 5122-5133) for rough heterogeneous electrodes is simplified for roughness features larger than the electrolyte screening length. The electrochemical impedance responses (EIS) of moderately rough polycrystalline Pt electrodes in NaNO3 electrolyte dissolved in aqueous and viscous media are analyzed and interpreted with the phenomenological theory. Experiments support predictions of theory for the EDL relaxation on rough and heterogeneous electrode, and also emphasize that the dynamics can be decomposed into compact layer and diffuse layer processes. Influence of viscosity is used to unravel the characteristic high frequency diffuse EDL dynamics through NaNO3 solution in 90% glycerol (by volume). These experiments also contrast the influence of concentration on EDL dynamics in aqueous and viscous media. EIS identifies four phenomenological regimes along with their characteristics frequencies. Finally, this phenomenological theory brings in significant physical insight and provides a useful method for interpreting experimental results. (C) 2017 Elsevier Ltd. All rights reserved.