Ensuring veridical spatial perception in immersive virtual environments (IVEs) is an important yet elusive goal. In this paper, we present the results of two experiments that seek further insight into this problem. In the first of these experiments, initially reported in Interrante, Ries, Lindquist, and Anderson (2007), we seek to disambiguate two alternative hypotheses that could explain our recent finding (Interrante, Anderson, and Ries, 2006a) that participants appear not to significantly underestimate egocentric distances in HMD-based IVEs, relative to in the real world, in the special case that they unambiguously know, through first-hand observation, that the presented virtual environment is a high-fidelity 3D model of their concurrently occupied real environment. Specifically, we seek to determine whether people are able to make similarly veridical judgments of egocentric distances in these matched real and virtual environments because (1) they are able to use metric information gleaned from their exposure to the real environment to calibrate their judgments of sizes and distances in the matched virtual environment, or because (2) their prior exposure to the real environment enabled them to achieve a heightened sense of presence in the matched virtual environment, which leads them to act on the visual stimulus provided through the HMD as if they were interpreting it as a computer-mediated view of an actual real environment, rather than just as a computer-generated picture, with all of the uncertainties that that would imply. In our second experiment, we seek to investigate the extent to which augmenting a virtual environment model with faithfully-modeled replicas of familiar objects might enhance people's ability to make accurate judgments of egocentric distances in that environment.