Context: Effective coordination between different functional contributors is fundamental for the success of collaboration-focused software development paradigms such as DevSecOps. However, the quantification of coordination in such environments has received limited attention. Objectives: We introduce a Multi-Class Socio-Technical Congruence metric MC-STC by extending the application of the widely studied Socio-Technical Congruence STC framework to address the above gap. Our metric enables assessing coordination in a setting where contributors with different functional roles or alignments collaborate. Using a large-scale exploratory case study, we evaluate MC-STC for two classes (i.e., 2C-STC) Methods: We calculated 2C-STC for 100 systematically selected projects from the TravisTorrent dataset, considering developers (dev) and security-focused developers (sf-dev) as the two types of contributors with different functional alignments (i.e. two classes). We hypothesised that the dev and sf-dev interaction would have a quantifiable impact on the Vulnerability Score (VS) of each project. Results: Our results show a moderate negative association between 2C-STC and VS, with the Spearman correlation reaching -0.427 (p = 0.00000624), indicating that higher levels of coordination between dev and sf-dev led to projects with a lower incidence of high-severity vulnerabilities. In addition, 2C-STC shows a stronger negative relationship with VS than STC, suggesting that it is the more sensitive indicator of this relationship. Conclusion: The specific instantiation of our proposed metric, 2C-STC, performs comparatively better than STC for measuring cross-functional coordination in our selected projects. However, further research is needed to explore its broader applicability.