The β"-alumina structure is important for sodium battery systems. Its structure is composed of layers of (111) oriented spinel-structure units separated by sodium containing conduction planes that are wide compared to the spinel units. Of critical interest is whether composition or structure modifications can be designed that would assist in speeding up the sodium conduction within these conduction planes. The present work looks at the geometric limitations to expansion or contraction of this conduction plane as we substitute different ions into the lattice in different sites. Clearly a wider or narrower plane could influence the conduction rate by influencing the sodium motion activation energy. We take a detailed look at the structure and specifically the oxygen atoms that "sandwich" the sodium conduction environment. These atoms (the O(3) and O(4) sites) are analyzed for different β"-alumina structures to understand the subtle but important changes that sodium ions may feel when diffusing in different compositions of this material.