We discuss the common hypothesis of complete graph representation according to which, in collaborative projects, all partners interact with each other in homogeneous ways.More precisely, this research aims to determine the heterogeneity in terms of existence and frequency of interactions between dyads of organizations that jointly participated in collaborative projects. From a survey of participants involved in innovation projects approved by a French cluster, we collect information about 754 collaboration ties. Using an ordered probit with selection equation, we then test the impact of several determinants, including geographical proximity, on the existence and frequency of the observed interactions.