Abstract This work presents an analysis of the functional derivative of the superconducting transition temperature T c with respect to the electron-phonon coupling function α 2 F ( ω ) [ δT c / δα 2 F ( ω )] and α 2 F ( ω ) spectrum of H 3 S ( <?CDATA $\mathrm{Im}\bar{3}m$?> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>Im</mml:mi> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> <mml:mo>̄</mml:mo> </mml:mover> </mml:mrow> <mml:mi>m</mml:mi> </mml:math> ), in the pressure range where the high- T c was measured (155–225 GPa). The calculations are done in the framework of the Migdal–Eliashberg theory. We find for this electron–phonon superconductor, a correlation between the maximums of δT c / δα 2 F ( ω ) and α 2 F ( ω ) with its higher T c . We corroborate this behavior in other electron–phonon superconductors by analyzing data available in the literature, which suggests its validity in this type of superconductors. The correlation observed could be considered as a theoretical tool that in an electron–phonon superconductor, allows describing qualitatively the proximity to its highest T c , and determining the optimal physical conditions (pressure, alloying or doping concentration) that lead to the superconductor reaching its highest T c possible.