The analysis of the capacitance incorporating the variations with the surface charge density of the image plane position and of the metal/solvent distance of closest approach is discussed. The relation with other theoretical models and with some recent experimental studies of the electrode/solution interface is analysed. The proper interpretation of the semi-empirical contribution for the solvent obtained by correcting the inner-layer capacitance by a theoretical contribution associated with the metal non-ideality is emphasized. The use of this semi-empirical contribution for discussing solvent orientation (different solvent with same electrode and vice versa) is finally considered.