The effect of the water pool size (omega degrees) on the average number of the probe molecules located at the interface and on the monophotonic ionization yield has been examined in anionic and cationic reverse micelles, using tetramethylbenzidine (TMB) as an easily photoionizable solute. The main conclusions of the present study are as follows : (1) The number of molecules located at the interface parallels that of the square radius of the water pool and partly depends on the compactness of the interface. (2) Owing to the high concentration of the counterions, the variations of the electrical potential remain low, when omega degrees increases from 18 to 40, although the fraction of free water increases significantly. (3) The charge separation efficiency (Y-TMB+) varies as the fraction of free water in the water pool. Such Y-TMB+ variations are interpreted in changes in the fundamental energy of the excess electron at the interface with omega degrees. (4) The comparison of Y-TMB+ values, obtained in the present work with previous data in direct micelles, points out the influence of the sign of the curvature radius on the photoionization reaction.