Metal nanoparticle catalysts dispersed on the surface of a perovskite oxide support show great promise in solid-state electrochemical devices for energy conversion and electrification of chemical processes involving hydrogen. Breakthrough (electro)catalyst performance and durability have been achieved by direct growth of nanoparticles from the oxide support by exsolution, and thus exhibit strong anchoring that inhibits agglomeration. Our hypothesis for explaining the observed results involves transition metals (TM) on interstitial positions in the perovskite structure, where small TM can dissolve into a square-planar configuration adjacent to A-site vacancies. The potential role of such interstitial solubility of TMs has so far not been addressed in understanding exsolution processes. The combined in situ XAS and total scattering data of synchrotron experiments will allow for a detailed model of short-range ordering and local distortions in certain cation environments.