Traditionally, heterogeneity levels have been associated with refuge availability and, consequently, with security areas for prey. Hence, there is assumed to be a positive correlation between the spatial distribution of potential victims and habitat heterogeneity levels. Among fish, the magnitude of predator-prey interaction has been associated with their size ratio, which includes body size as a central variable for individual predation risk. To date, the importance of body size and its interaction with spatial heterogeneity in relation to fish spatial distribution has been scarcely considered, being this the main objective of the present study. Based on a semi-experimental design, defined by the level of spatial heterogeneity, censuses in 24 artificial pools were conducted for 2 years at the rocky intertidal zone. This study focused on carnivorous fish assemblages residing off the rocky shore of central Chile. The results indicated a counterintuitive response of fish to spatial heterogeneity, with a higher abundance of small fish in open areas. Apparently, this differential distribution could be related to the size ratio between prey and predator (size-dependent susceptibility to predation), which is a hypothesis supported by decreases in the co-occurrence of fish with increasing size similarity.