The Coulomb effect hypothesis, formerly used to interpret fluctuations in the curve of maximal total kinetic energy as a function of light fragment mass in reactions 233U(nth,f), 235U(nth,f), 239Pu(nth,f), is confirmed in high kinetic energy as well as in low excitation energy windows, respectively. Data from reactions 233U(nth,f), 235U(nth,f), 239Pu(nth,f) and 252Cf(sf) show that, between two isobaric fragmentations with similar Q-values, the more asymmetric charge split reaches the higher value of total kinetic energy. Moreover, in low excitation energy windows, between two isobaric charge splits with different Q-values, the more asymmetrical fragmentations is preferred.