Nascent augmented reality/mixed reality (AR/MR) experiences are emerging across the Department of Defense (DOD) training and operational ecosystems. Immersive AR/MR experiences can garner cognition efficiencies in simulation or in battlespace, but designing for immersion and increased presence has proven elusive across this bourgeoning arena. The obscurity is due in part to a lexicon built for fully synthetic virtual reality (VR) experiences. As an example, the term presence in VR is often associated with a feeling of “being there” in a remote synthetic location; however, in AR/MR, “there” is often right where you are, so defining presence becomes more nuanced. Beyond problematic terminology, AR/MR experiences have expanded the boundaries of how users engage and spatially interact with synthetic content and conversely, how synthetic content interacts with the intrinsic physical environment. This paper explores how optimizing for passive spatial interactivity, in particular environmental interactions at the seam of the physical and synthetic boundary unique to AR/MR, will maximize a holistic sense of presence through a proposed theory of environment extension, ultimately leading to enhanced immersive experiences. Borrowing from the concept of “self-extension” (Belk, 1988), the author contends that environment extension can be leveraged to passively establish environmental presence by influencing the user’s physical surroundings and manipulating the individual’s subconscious feeling of extended self-identity. Different types of spatial interactivity and their utility in enhancing presence in AR/MR environments are discussed, followed by several recommendations on passive environmental interactivity strategies. By exploiting immersive AR/MR experiences by way of passive environmental interactions, the DOD can expect better learning outcomes through an improved affective training medium, as well as increased productivity in the office or in battle by offloading cognition.