Quantum random numbers generators (QRNGs) rely on quantum systems to produce sequences of random numbers with an overall lower level of predictability than classical algorithmic systems. Over the past two decades, phase randomizations of coherent sources from quantum spontaneous emission effects have gained a lot of interest due to their operational simplicity, cost-contained components, and ability to generate random numbers at high rates. However, many QRNGs require optimal calibration and alignment to ensure efficient and effective random number generation. This work demonstrates a detailed analysis of a heterodyne measurement based QRNG, which implements phase randomization from two independent laser sources. The analysis also quantifies the effects of setup misalignments using the Kullback-Leibler divergence as a benchmark to assess the limiting conditions of secure random number generation.