In the present study, we have employed two dimensional ASYNNNI model to investigate how the Ortho-II structure formation influences doping, p, of the superconducting CuO2 planes in YBa2Cu3O6+x high-Tc superconductor. It was shown, that if the direct repulsive interaction between next nearest oxygen atoms (V3), present in the Hamiltonian of the ASYNNNI model, is neglected, the Ortho-II ordering is destroyed and doping p becomes a linearly increasing function of oxygen concentration x in the range 0.50⩽x⩽0.65, for any choice of critical chain length lcr (defined so that CuO chains of length l<lcr cannot transfer holes to the CuO2 planes). Consequently, the Tc(x) dependence, obtained by the employment of the universal Tc vs. p relation, does not exhibit experimentally observed “60K plateau”. The results presented here confirm that establishment of Ortho-II structural phase is a key factor for the “60K plateau” formation in the Tc(x) dependence.