Two current assumptions of the Zeesluisformulering (ZSF) regarding a homogeneous lock density and instantaneous shipping are tested against refined descriptions according to literature: a stratified lock density and shipping according the continuity approach. These are implemented into a conceptual model constructed in Python, after which optimizations are quantified by means of a sensitivity analysis and a case study. It was found that by using the new assumption set, a maximum of approximately 10% less salt intrusion is obtained as a result of the influence of the return current on the lock exchange.