Augmented Reality (AR) has shown great potential for supporting co-located collaboration. Yet, it is rarely articulated in the design rationales of AR systems that they promote a certain socio-spatial configuration of the users. Learning from proxemics, we argue that such configurations enable and constrain different co-located spatial behaviors with consequences for collaborative activities. We focus specifically on enabling different collaboration styles via the design of Handheld Collaborative Augmented Reality (HCAR) systems. Drawing upon notions of proxemics, we show how different HCAR designs enable different socio-spatial configurations. Through a design exploration, we demonstrate interaction techniques to expand on the notion of collaborative coupling styles by either deliberately designing for aligning with physical reality or going beyond. The main contributions are a proxemics-based conceptual lens and vocabulary for supporting interaction designers in being mindful of the proxemic consequences when developing handheld multi-user AR systems.