A parameter of the P,T -odd Hamiltonian characterizing interaction of the nuclear Schiff moment with the gradient of electronic density on the Xe nucleus is calculated for an isolated Xe atom and for liquid xenon. We use a more realistic model of liquid medium than the spherical cell model used by Ravaine and Derevianko [Phys. Rev. A 69, 050101(R) (2004)]. Qualitatively different results for enhancement of the P,T -odd effect in liquid xenon are obtained when polarization of the medium is taken into account. Thus, proper choice of the liquid phase model is crucially important even for calculation of the properties dependent mostly on the electronic density near a nucleus.