This paper investigates the growth of the most massive cosmological objects. We utilize the Simsilun simulation, which is based on the approximation of the silent universe. In the limit of spatial homogeneity and isotropy, the silent universes reduce to the standard Friedmann-Lemaître-Robertson-Walker models. We show that within the approximation of the silent universe the formation of the most massive cosmological objects differs from the standard background-dependent approaches. For objects with masses above 1015  M⊙, the effect of spatial curvature (overdense regions are characterized by positive spatial curvature) leads to measurable effects. The effect is analogous to the effect that the background cosmological model has on the formation of these objects (i.e., the higher the matter density and spatial curvature, the faster the growth of cosmic structures). We measure this by means of the mass function and show that the mass function obtained from the Simsilun simulation has a higher amplitude at the high-mass end compared to a standard mass function such as the Press-Schechter or the Tinker mass function. For comparison, we find that the expected mass of most massive objects using the Tinker mass function is 4.4-0.6+0.8×1015  M⊙, whereas for the Simsilun simulation it is 6.3-0.8+1.0×1015  M⊙.