An experimental analysis of the effect of size variation for a cylindrical-shaped bluff body in flow-induced vibration (FIV) for the purposes of harvesting ambient energy is explored in this study. The research was conducted at a very low Reynold’s number in a closed-loop tunnel operating at a very low speed. An investigation of the power generation potential achieved by varying the size of the bluff body was conducted. A comparative study is also presented for varying the diameter configuration against the distance of the energy-harvesting piezoelectric flag from the cylindrical bluff body. At distances other than the optimal distance of the piezoelectric harvester from the bluff body, reduced efficacy of the power generation is observed. The results show a 17% increase in power with the use of 2x the size of the reference bluff body.