This study aims to investigate the nature of the hindrance to complete fusion in heavy-ion collisions at energies near the Coulomb barrier. The research focuses on how the competition between compound nucleus (CN) formation and the quasifission process is influenced by the mass asymmetry of the entrance channel and the geometric alignment of the colliding nuclei. The formation and breakup of the dinuclear system (DNS) were calculated using the DNS model as a function of orientation angles and orbital angular momentum. The model incorporates a transport master equation to describe nucleon transfer from the light fragment to the heavy one, accounting for excitation energy \(\varvec{E}_{\varvec{Z}}^{\varvec{*}}\) and the potential energy surface (PES). The theoretical mass distributions were compared with experimental data for \(^{\varvec{48}}\) Ca + \(^{\varvec{168}}\) Er ( \(\varvec{E}_{{\textbf {lab}}}=\varvec{194}\) MeV) and \(^{\varvec{12}}\) C + \(^{\varvec{204}}\) Pb ( \(\varvec{E}_{{\textbf {lab}}}=\varvec{73} \) MeV) reactions, leading to the formation of \(^{\varvec{216}}\) Ra with the same excitation energy \(\approx \) 40 MeV. In these data quasifission yields were extracted by separating the fusion-fission component ( \(\varvec{Y}_{{\textbf {FF}}}\) ) from total binary yields using multi-Gaussian fitting. Quasifission yields are strongly dependent on the relative orientation of the symmetry axes. Elongated tip-to-tip configurations (small orientation angles) significantly favor quasifission over CN formation due to a higher intrinsic fusion barrier \(\varvec{B}_{{\textbf {fus}}}^{\varvec{*}}\) . In the less mass asymmetric \(^{\varvec{48}}\) Ca + \(^{\varvec{168}}\) Er reaction, the quasifission yield is approximately one order of magnitude higher than in the highly asymmetric \(^{\varvec{12}}\) C + \(^{\varvec{204}}\) Pb system. While the \(^{\varvec{12}}\) C-induced reaction leads to fusion with near-unity probability, the \(^{\varvec{48}}\) Ca + \(^{\varvec{168}}\) Er system is dominated by quasifission. The results confirm that the hindrance to complete fusion is primarily driven by the quasifission process, which acts as a major drain on the fusion channel. The relative alignment of deformed nuclei is a decisive factor, particularly in more symmetric entrance channels where elongated configurations act as a bottleneck for fusion. These findings provide critical insights for optimizing the synthesis of superheavy elements by identifying the most favorable collision geometries and mass asymmetries.
