Extreme heat challenges the liveability of cities. Urban parks are popular as an efficient mitigative solution; however, uncertainties remain regarding whether and how the spatial configuration affects the effectiveness in practice. This paper tackles this issue by comparing the microclimatic amelioration potential of urban parks with the same green ratio in different spatial configurations. The study was conducted using microscale climate simulation in ENVI-met within three highly developed urban settings in Melbourne City, Australia, on 30th January 2009, during one of the most intense heatwave events. Hourly simulated data were extracted from all outdoor grids, encompassing nine heat-related indices, including meteorological variables, thermal comfort variables, and energy balance components. Linear mixed models were used to assess the effect of spatial configuration on improving outdoor thermal conditions. The results highlight a significant influence of spatial configuration in microclimate amelioration, and that these effects were context-specific, and no universally effective design emerged across locations, even within the same city. The findings underscore the necessity of considering other factors, such as surface cover characteristics and building configurations, and emphasise the importance of conducting site-specific simulations when introducing green infrastructure for heat mitigation.