Gram-negative bacteria and allows to inject toxins directly into adjacent cells. Pseudomonas aeruginosa is an opportunistic pathogen and uses T6SS for bacterial competition that allows it to establish and persist within dense polymicrobial biofilm communities. P. aeruginosa possesses 3 distinct T6SSs and a set of more than 20 toxic effectors with diverse functions including disruption of cell wall integrity, degradation of nucleic acids, or metabolic impairment. We generated a collection of mutants with various degrees of T6SS activity and/or sensitivity to each of the individual T6SS toxins and through disruption of genes encoding Gac-Rsm cascade components we generate a set of strains with graduated T6SS activity and killing capacity. By imaging whole mixed bacterial macrocolonies, we observed that the efficacy of individual T6SS toxins is highly variable and synergistic use maximises impact on prey growth. We show that competition mediated by as little as a single toxin delivered at low doses enables restriction of prey bacterial expansion while increase in toxin delivery rate enables a near complete elimination of prey bacteria. Remarkably, the degree of intermixing between prey and attacker populations is also key determinant of the competition outcome, as active intermixing promotes the frequency of contacts between competitors, and prey populations can use type IV pili-dependent twitching motility to move away from the attacking population. Finally, we implemented a computational model to better understand how changes in T6SS firing behaviours or cell-cell contacts lead to population-level competitive advantages. Overall, furthering the understanding of how highly local contact-based interactions between individuals shape the structure of whole populations, thus providing conceptual insight applicable to all types of contact-based competition.