A parametric study on the stability performance of a prototypical natural circulation BWR is performed with the downscaled GENESIS facility. The GENESIS design is based on fluid-to-fluid modeling and includes an artificial void reactivity feedback (VRF) system for simulating the neutronic-thermal-hydraulic coupling. In this work a more sophisticated VRF system than its predecessors is developed and implemented. The VRF allowed investigating different configurations relevant for the reactor design. The experiments show that changing the fuel rods diameter to a half (doubling) decreases (increases) the stability performance of the system while the resonance frequency increases (decreases). In addition, it is found that the use of MOX fuels in a BWR slightly decreases the stability performance of the reactor. On top of this, it is clearly observed that at least two oscillatory modes exists in the system, the thermal-hydraulic mode (associated to density waves traveling thorough the core plus chimney section) and the so-called reactor mode (related to density waves travelling thorough the core). It is observed that the last one is amplified by increasing (in an absolute sense) the void reactivity feedback coefficient. Details regarding the interplay between these oscillatory modes is also given.