We investigate the variations of modal properties of 12-fold quasiphotonic crystal microcavities sustaining whispering-gallery (WG) mode with different central post sizes both in simulations and experiments. We realize our design by a series of dry- and wet-etching processes. WG mode lasing actions are obtained with high quality (Q) factor of 8,400 from microcavity with effective post size 420 nm in diameter. Loss and thermal behaviors are analyzed by measured Q factors, thresholds, and rolling-off effects from light-in light-out curves of microcavities with increased post size. By finite-element simulations, we also address the heat sink improvement due to presence of larger central post that is observed in measurements.