We also considered the internal space present in the crystal structure of the candidate electrides and find that the design principle of larger pore appears for hosting anionic electrons valid up to a previously unreported cut-off of around 3 angstroms. Several of the confirmed electrides conform to this design rule right up to the latter end of the scale. Whether the electrides with this internal distance of around 3 angstroms are disproportionately confirmed in experiment because the largest pore sizes are easier to characterise in experiment or this distance has an intrinsic significance to anionic electron species warrants further investigation.