Second screening - engaging with a mobile device while watching TV - is ubiquitous. Previous research demonstrates that this is hampered by cognitive and physical disjuncts between the simultaneous content streams. To engage effectively with more than one screen, users must manage their attention, for example, by frequently adjusting their gaze or posture. This can lead to cognitive effort, which leads to disengagement, content sacrifice, and ultimately, affects user experience (UX) negatively. In this paper, we look to improve the design of the dual-screen scenario through \emph{display commonalities}; the mirroring of one content stream (e.g., TV material or second screen content) within the other. We evaluate this design space with professional broadcast practitioners, and then conduct an empirical investigation to determine the impact of the most successful methods towards understanding their impact, and designing towards positive UX with multi-device scenarios
