The identification of a parameter (ALPHA) which governs the torsional behavior of linear elastic one-storey eccentric systems, allowed to introduce a synthetic procedure (ALPHA method) for evaluat-ing the maximum rotational response of such systems under seismic excitation. This paper aims at investigat-ing the predictive capabilities of the method, focusing mainly on the absence of synchrony between the maxi-mum longitudinal displacement and the maximum rotation of the Centre of Mass, and on the evaluation of the maxima displacements of the systems corner points (flexible side). The analysis, performed on systems sub-jected to uniaxial seismic excitation, have been conducted with 218400 numerical simulations. The results ob-tained allows: (i) to identify a simple correlation between the effective torsional systems response, and (ii) to determine a synthetic formulation which allows to evaluate the maximum displacement of the flexible side as a function of the maximum values of the longitudinal displacement and of the rotation.