Optimization of the performance of vanadium redox flow batteries (VRFBs) is closely related to flow rate control: a proper flow rate adjustment reduces the losses and extends the battery lifetime. In this regard, the so-called flow factor control strategy of VRFBs has been recently proposed in the literature and some numerical/experimental validations have been performed. The strategy is a generalization of Faraday's first law of electrolysis as it uses a special scaling parameter referred to as the flow factor. In our paper, we show how this factor is related to the conversion rate (fraction conversion per pass) and geometrical properties of the battery. Finally, we investigate the flow factor as a function of the fraction conversion per pass and stack/tank volumes, and perform numerical simulations to confirm the theoretical results.