Due to the important role of cocatalyst in the polymerization process employing industrially favored Ziegler-Natta catalysts, its effect on kinetic behavior, catalyst activity, and polymer properties is discussed. In this paper triethyl aluminum (TEA) and triisobutyl aluminum (TIBA) have been used as the main cocatalyst ingredient with 10-20 mole percent of diethyl aluminum chloride (DEAC) and ethyl aluminum dichloride (EADC) cocatalysts. Among studied systems, neat TEA demonstrated the highest activity. Moreover, TEA-DEAC and TEA-EADC cocatalysts revealed a built-up kinetic profile, while TIBA-DEAC and TIBA-EADC show a decay-type kinetic curve. According to melt flow index results, no considerable change in flowability was detected in the synthesized polyethylenes (PE). On the other hand, the ethylene insertion and chain termination mechanisms were scrutinized by means of density functional calculations using Ti active center located in (110) and (104) facets of the MgCl2 surface. Results revealed that TiCl4 supported (110) termination favors the PE chain production, being the ethylene insertion, the rate-determining step. To shed light on the bulkiness level of employed cocatalysts, buried volume (VBur) together with the two-dimensional map of cocatalyst molecules were considered. Higher VBur of TIBA can explain its lower activity and decay type kinetic profile obtained in the experimental section.