While characterizing the mechanical behavior of granular assemblies through DEM simulations, various macro and micro level heterogeneities are often encountered. Such macro level heterogeneities may arise due to stress and void concentration near the wall boundaries; whereas, the micro level heterogeneities are attributed to consideration of only limited number of particles within the representative volume element (RVE). The present study assesses these macro and micro level heterogeneities in reference to the mechanical characterization of sand in DEM-based biaxial test simulation with both rigid and flexible lateral boundaries. In this regard, stresses and strains have been calculated using a wall-based global estimation and a representative area element (RAE)-based local estimation. It has been suggested that the RAE should occupy a maximum of 90% area of the specimen in order to avoid any macro level heterogeneity and can still be able to capture its overall mechanical behavior. For obtaining the spatial variation of field variables, RAE of smaller diameters are often employed. In such cases, depending on the average particle size of the granular assembly and the specimen dimensions, the diameter of the RAE should be selected ensuring that it is small enough to aptly capture the local variation of field variables and at the same time, large enough to avoid any micro level heterogeneity.