Abstract We investigate marine stratocumulus cloud radiative sensitivity to meteorological and aerosol controlling factors in a perturbed parameter ensemble of the Energy Exascale Earth System Model version 3 (E3SMv3). The ensemble perturbs 25 cloud, convection, and aerosol parameters, spanning diverse cloud behavior. The default simulation and many ensemble members capture observed responses to most controlling factors, but not to surface temperature advection, revealing a structural deficiency in processes linking stratocumulus to advection. Many members also overestimate cloud fraction and radiative responses to inversion strength, free‐tropospheric humidity, and sulfate aerosol optical depth. Differences in mean cloud optical depth substantially modify the radiative impact of similar cloud fraction changes, showing that the mean cloud state strongly regulates stratocumulus radiative sensitivity. Across the ensemble, conversion of cloud water to rain controls mean optical depth, identifying autoconversion as a key microphysical control on stratocumulus radiative sensitivity.