Triblock rod-coil oligomers with bulky coil blocks were previously utilized to create self organized mushroom-shaped nanoaggregates. The boundary effects in such small aggregates and the steric repulsions due to close packing of bulky coil blocks lead to highly perturbed, nonideal systems. We describe here a coarse grained model to understand the properties of such systems. This model is based on enumeration of chain conformations on a lattice to calculate entropy loss due to aggregation. We studied the contribution of chain architecture and crystallization enthalpy on equilibrium properties such as size, size distribution, and thermodynamic stability for a mushroom-shaped constrained structure. In agreement with previous theoretical work for other finite architectures, our study verified that aggregate size is determined by the competition between entropic and enthalpic contributions from different blocks. Most importantly, polydispersity of the nanoaggregates was found to decrease as bulkiness of the coil block structural unit is increased and also as surface energy of the rod block crystal is increased. These results suggest that branched coil architectures such as dendrons could be utilized to further improve the structural properties of the aggregates.