[en] Asymptotic behaviour near phase transitions can be suitably characterized by the scaling of Δs/Q² with ε = 1 - T/T_c, where Δs is the excess entropy and Q is the order parameter. As Δs is obtained by integration of the experimental excess specific heat of the transition Δc, it displays little experimental noise so that the curve log(Δs/Q²) versus log ε is better constrained than, say, log Δc versus log ε. The behaviour of Δs/Q² for different universality classes is presented and compared. In all cases, it clearly deviates from being a constant. The determination of this function can then be an effective method to distinguish asymptotic critical behaviour. For comparison, experimental data for three very different systems, Rb₂CoF₄, Rb₂ZnCl₄ and SrTiO₃, are analysed under this approach. In SrTiO₃, the function Δs/Q² does not deviate within experimental resolution from a straight line so that, although Q can be fitted with a non mean-field exponent, the data can be explained by a classical Landau mean-field behaviour. In contrast, the behaviour of Δs/Q² for the antiferromagnetic transition in Rb₂CoF₄ and the normal-incommensurate phase transition in Rb₂ZnCl₄ is fully consistent with the asymptotic critical behaviour of the universality class corresponding to each case. This analysis therefore supports the claim that incommensurate phase transitions in general, and the A₂BX₄ compounds in particular, in contrast with most structural phase transitions, have critical regions large enough to be observable