Postsecondary STEM instruction often does not meet the diverse needs, abilities, and interests of postsecondary STEM learners. The Universal Design for Learning (UDL) framework provides ideas for designing instructional environments to support learner variation. However, existing tools do not meet the professional development needs of many postsecondary STEM instructors, or the research needs of some discipline-based education researchers. Enacting and assessing UDL in postsecondary STEM requires expertise form three stakeholder groups: postsecondary STEM instructors, experts in disability and UDL, and discipline-based education researchers. Building on prior work with UDL in postsecondary STEM, our multi-disciplinary team developed the Universal Design for Learning Instructional Practice Observation Protocol (UDL-IPOP). The UDL-IPOP has one-to-one alignment with the finest-grain descriptors (i.e., checkpoints) in the UDL framework as well as exemplar practices to explicate UDL-aligned instructional practices for postsecondary STEM. After drafting an initial version of the UDL-IPOP, we discussed it with representatives from the three relevant stakeholder groups. Here, we describe practices that aligned with the UDL framework. Then, we discuss initial impressions about which practices postsecondary STEM instructors likely already implement and ideas from disability experts about how STEM instructors could deepen their UDL practice. Overall, we find that postsecondary STEM instructors and disability experts focused on different types of learner variation. We suggest that collaborating with disability experts could provide a necessary "lens change" to better support variation in postsecondary STEM learners' needs, abilities, and interests.