Using two-particle interferometry, the STAR collaboration has characterized the geometric substructure of the particle-emitting source for all energies and colliding systems at RHIC. We present systematic studies of neutral and charged meson interferometry. Strong collectivity is revealed through the $m_T$ dependence of HBT radii for all particle types. Preliminary results suggest a scaling in the pion HBT radii with overall system size, as central Au+Au collisions are compared to peripheral collisions and even with d+Au and p+p collisions, naively suggesting comparable flow strength in all systems. To probe this issue in greater detail, multidimensional correlation functions are studied using a spherical decomposition method. This allows clear identification of source anisotropy and, for the light systems, the presence of significant long-range non-femtoscopic correlations. Uncertainties due to non-Gaussian components of the correlations are addressed and quantified.