An attempt has been made to have exclusive information on effect of various entrance channel parameters on the onset of incomplete fusion in heavy ion induced reactions at energies at 4 7 MeV/A. A number of experiments have been performed by our group to measure the excitation function and forward recoil range distribution of various evaporation residues populated via complete fusion and/or incomplete fusion of O with different targets. The experimental excitation functions have been analysed in the frame work of compound nucleus decay using statistical model code PACE-4. Analysis of data suggests the existance of incomplete fusion even at energies as low as near barrier energies where complete fusion is supposed to be the sole contributor. Further more, in order to understand incomlete fusion reactions in a more conclusive way, the incomplete fusion fraction has been analyzed with the existing data for αcluster projectiles with different targets of low, medium and heavy mass region. The study of percentage incomplete fusion fraction for different projectile target combinations deduced from experimentally measured excitation functions of individual reaction product shows strong dependence on projectile energy, mass asymmetry of interacting partners and α−Q value of the projectile.