The asymmetric triangle (fronting or tailing) concentration profiles and their broadening are the typical results of the electromigrational zone dispersion characterizing a system of the analyte in the background electrolyte (BGE). The present contribution suggests the parameter named the relative velocity slope, S-BGE,S-X, which was introduced here as a quantity characterizing the peak broadening and the asymmetry. S-BGE,S-X vs. analyte ionic mobility diagrams are suitable for the comparison of BGE(S) of given pH and the conductivity composed of electrolytes of different pK(a)s and ionic mobilities. The concept of S-BGE,S-X diagrams is verified by capillary zone electrophoresis of the model analytes, which involve (i) the series of sulfobenzoylated poly(ethylene glycols) as examples of the strong electrolytes with different ionic mobilities and (ii) the series of monobasic phenols as weak electrolytes with different pK(a)s and similar ionic mobilities. It follows from both theoretical predictions of peak symmetry and their experimental verification that the optimum composition of BGEs is determined mostly by the suitable ionic mobility of the colon in dependence on the ionic mobility of the analyte. The low-conductivity BGEs based on low-molecular carrier ampholytes are at best only comparable with the properly chosen monobasic electrolytes.