Visualization of complex architectural and interior design proposals demands spatial perspective taking (SPT), an ability that can be difficult to acquire. Mixed Reality (MR) is particularly effective in architectural visualization because it overlays virtual models onto already existing real environments, allowing for precise spatial accuracy and aesthetic assessment. However, MR confines users to viewpoints tied to locations they can physically reach in the real-world. To overcome this constraint, we designed an applied, visibility-driven SPT task and explored two methods to provide additional perspective cues in MR: the World-in-Miniature (WIM) mode and the Cross Reality (CR) mode. The WIM mode provides a scaled-down 3D replica of the virtual environment, allowing users to explore a design at a reduced scale. Conversely, the CR mode allows switching from MR to VR to hide the real-world completely, enabling users to teleport to physically unreachable viewpoints and assess a design at an accurate scale. We conducted a pilot user study with 14 participants and a formal user study with 80 participants on an object-placement task. Our results revealed that the CR mode achieved success scores as high as those of the WIM mode. The WIM mode was faster and perceived as more user-friendly. However, participants preferred the CR mode for its accurate spatial representation and effective presentation of design ideas. The CR mode recreates the physical room as a scale-accurate virtual counterpart, preserving geometric cues critical for spatial visualization while removing the need for manual room modeling. Our findings highlight the potential of these modes to transform 3D design visualization and set new standards in the industry.