Background: The role of hexadecapole deformation (β4 ) in sub-barrier fusion has been studied for the 16 O+174,176 Yb reactions; however, the extracted β4 values are model-dependent and carry systematic uncer- tainties that remain unresolved. Purpose: We extend fusion cross-section measurements to the 16 O+170,172 Yb reactions to investigate isotopic dependence of fusion excitation functions and to clarify the role of higher-order static deformations across the complete 16 O+170,172,174,176 Yb isotopic chain. Method: Evaporation residue (ER) cross sections for 16 O+170,172 Yb were measured from 12 % below to 35 % above the Coulomb barrier using the Heavy Ion Reaction Analyzer (HIRA) at IUAC, New Delhi. The data are analyzed within the coupled-channels and statistical model frameworks. Results: A strong sub-barrier fusion enhancement is observed relative to one-dimensional barrier penetration model (1D-BPM) predictions. Coupled-channels calculations incorporating quadrupole and hexadecapole defor- mations of the target nuclei reproduce the measured fusion excitation functions for both reactions. Statistical model calculations with a single fission barrier scaling factor kf = 1.10 reproduce the ER and fission cross sections simultaneously, over the entire measured energy range. The single-Gaussian barrier distribution analysis shows that 16 O+174 Yb exhibits the largest sub-barrier enhancement among the 170,172,174,176 Yb nuclei. Conclusions: Coupled-channels calculations including both quadrupole β2 and hexadecapole β4 deformations of the target nuclei successfully reproduce the measured fusion excitation functions for 16 O+170,172 Yb. Our Analysis brings out the role of β4 across the entire range of Yb nuclei. The reproduction of ER and fission excitation functions with kf = 1.10 rules out non-compound nuclear fission (NCNF) contributions for both systems. The pronounced sub-barrier enhancement in 16 O+174 Yb is attributed to the midshell character of 174 Yb (N = 104), where nuclear collectivity is maximal.