In SAFe, story point sizing is a collaborative process that involves the entire Agile Team. The Product Owner, even with domain expertise, should respect the team's process and support their decision on sizing. This is because the team's estimate reflects their understanding of the work and their capacity to complete it. The Product Owner's role is to provide clarity and answer questions about the user story, not to dictate the size of the story. This approach ensures that the team remains empowered and that estimates reflect the team's perspective, leading to more accurate planning and tracking. It's important to note that the Product Owner can contribute to the discussion by sharing their expertise, but the final decision on story points should be a team consensus1.