The rise of remote work has reshaped how design teams collaborate, introducing challenges in replicating the benefits of in-person collaboration. As remote collaboration normalized, accelerated by the COVID-19 pandemic, new challenges emerged that had previously gone unnoticed. Among these, designers report the loss of co-exploration, the experience of iteratively exploring prototypes, ideas, and concepts together. Prior research has identified five patterns of co-exploration, demonstrating its functional and social value in collaborative design. However, because that research was conducted in educational settings, it remains unclear whether the five co-exploration patterns also reflect the experiences of professional designers, and how such co-exploration should be supported in remote design activities based on expert perspectives. To explore these questions, we interviewed design experts to examine how the five co-exploration patterns apply in both co-located and remote settings. While they described a variety of challenges in remote collaboration, our analysis showed how remote collaboration affects both the execution and quality of co-exploration. These findings informed a speculative ideation process, in which experts used Inspiration Cards to propose solutions grounded in practice. Their insights revealed the importance of shaping conditions that support co-exploration through the coordinated use of people, materials, and interactions. These findings led to the development of the Designing Tools for Co-exploration (DTC) guideline, which provides intermediate-level design knowledge to guide tool creation and help design teams strengthen their collaborative practices.