Hierarchical modulation is a means to better use the overall resources of a given system by superposing, in terms of modulation, a user with better radio conditions on one with inferior radio conditions so as to advantageously transfer some resources from the latter to the former. This in turn impacts the overall performance of the system, which we consider in this work at the flow level, for a realistic dynamic setting where users come to the system and leave it after a finite duration corresponding, for instance, to the completion of a file transfer. We quantify, in this work, analytically and via simulations, the gain thus achieved and propose a new scheme in which users with bad radio conditions are also superposed on ones with better radio conditions so as to enhance the system performance even further