Using synergistic frameworks such as Standpoint Theory, Domains of Power (DoP), and the Holistic Ecosystem for Learning Physics in an Inclusive and Equitable Environment (HELPIEE), we analyzed how those in the position of power, e.g., instructors, can play important roles in establishing and maintaining safe, equitable, and inclusive environments for students by comparing three studies. This is especially important for historically marginalized students such as women and ethnic and racial minority students in physics. The first study is Johnson's 2020 study using DoP framework to investigate physics culture and identity of students and faculty at a small predominantly White liberal arts college. This study describes a physics department that other departments should try to emulate. The second study is Santana and Singh's 2023 study which utilized Standpoint Theory to understand the experiences of undergraduate women at a large predominantly White research institution and revealed a masculine physics culture in which women felt marginalized. The third study is Santana and Singh's 2024 study which combined Standpoint Theory, DoP, and the HELPIEE frameworks to investigate undergraduate women's experiences at a mid-sized physics department at a small predominantly White private liberal arts college. This comparative case study highlights the differences and similarities amongst three US institutions of different types with regard to their physics cultures and the role of instructors' equity-focused goals in shaping undergraduate women's experiences. These findings can help physics departments contemplate how to improve their own physics culture and make it equitable and inclusive.