The Large-Eddy Simulation (LES) approach is used to model partially-premixed combustion (PPC) in confined and unconfined fuel vapor clouds. The model is based on the concept of a filtered reaction progress variable to describe the premixed combustion. The premixed combustion model is implemented into the Fire Dynamics Simulator (FDS), developed at the National Institute of Standards and Technology, USA, and is coupled with either an equilibrium-chemistry, mixture-fraction based model (FDS Version 4) or an eddy dissipation model (FDS Version 5) for non-premixed combustion. Modifications to the model are developed and implemented with the goal of reducing the grid resolution requirement while still producing physically sound results. The modified formulation is tested using both versions of the non-premixed combustion model, and the results are compared. It is found that the modifications are capable of reducing errors associated with poorly-resolved simulations in both versions of the model.