[en] The method of data analysis proposed by Miettinen and Pirilae which eliminates kinematic reflections in the variation of the slope in momentum transfer distribution, as a function of diffractively produced effective mass, is applied to the reaction K⁺p→K⁺π⁺ π^-p at 4.97 GeV/c. It seems that for this reaction and at this energy, the strong rise of the slope parameter observed for low mass K⁺ π⁺π^- systems is mostly produced by kinematic effects. There is no proof that a slope-mass correlation must be explicitly present in the invariant matrix element. This does not confirm the results obtained by Miettinen and Pirilae for the reaction pp→nπ⁺p at 19 GeV/c. (author)