The systematic comparison of the crystal structures of the BEDT-TTF salts with the planar anion layers elucidated that the pattern of the openings in the anion layer governs the packing motif of the donor molecules. On the ambient pressure BEDT-TTF superconductors, an almost linear relationship between the V(mes2) and Tc was found out, where V(mes2) is the estimated volume of the space, mainly in which the carrier can distribute.