The bottom electrode (heater) in a mushroom cell phase change memory (PCM) is one of the major components which determines device performance. Understanding the effect of heater geometry on Reset characteristics is necessary for engineering and fabricating efficient structures. In this paper, we explore the role of certain geometrical parameters of the heater using computer simulations. Performing such parameter sweeps experimentally would be uneconomical and time consuming. Our results indicate that the heater top radius/area is of utmost importance for Reset Current and cross-sectional area of the heater matters more that the actual shape of the cross-section. The focus of this paper is to provide a qualitative understanding of the variation of quantities of interest as the heater configuration is changed.