We provide new theoretical arguments which together with recent measurements by Gong et al. [1996], strongly support the existence of the jet flow regime [Giménez-Curto and Corniero, 1996]. The theoretical arguments refer in particular to the introduction of a formal condition for flow separation from uneven surfaces for laminar and turbulent flow as well. This condition, which is a first requirement of the jet regime flow model, is compared with existing information.