The paper investigates corona onset models proposed in the literature. Initially, the models and their limits of application are discussed. Different factors such as the electric field (E-field) distribution around the electrodes and their surface conditions are taken into account. The models are then numerically and experimentally evaluated for different point-plane arrangements. The results show good agreement for situations where highly non-uniform fields occur. Additionally, a model based on the Field Efficiency Factor (FEF) is also analyzed. An adjustment at the FEF, based on the experimental results, is proposed.