For the purpose of exploring the usefulness of short simulations for efficient model evaluation and tuning, we have conducted 31x128 CAPT hindcasts for July of 2008 and carried out a parametric sensitivity analysis using a surrogate model. The ACME-atmosphere model's sensitivity to uncertain parameters in the turbulence and shallow convection parameterizations is analyzed along the GPCI cross-section which features cloud regime transitions from stratocumulus to shallow cumulus and deep cumulus. We present the dependence of model sensitivity on cloud regime and simulation time, and discuss the implications on the potential use of short simulations for model tuning.