Using arrays of coupled vibration energy harvesters has become a prominent trend in energy harvesting research due to its ability to cover a wider frequency range and high-power production. In our investigation, we have studied a series of spring-coupled cantilever energy harvesters and discovered the effect of coupling stiffness on the system's dynamics and energy harvesting capability. The study found scope for enhanced energy harvesting from targeted frequencies by designing custom stiffness distribution. Moreover, this study also investigates the effect of beam modeling on the numerically obtained performance of the harvester. Modeling large deformation of cantilever beams using inextensible conditions induces a nonlinear inertia effect in the governing equations. The results demonstrate a nontrivial trend that favors a small range of spring stiffness values for the best harvesting performance. An analysis using the multiple-scale method (MMS) has been reported to explain the results of the numerical simulations. This reveals that spring coupling directly affects the modeling-induced inertial nonlinearity at a particular stiffness. This qualitatively changes the system's dynamics from a hardening to a softening one. Ultimately a comparative study has been conducted with harvesters of different sizes, and the obtained results point towards a size-independent optimum grounding stiffness for efficient energy harvesting.