We investigated YBa2(Cu1?zMz)3O7-? (MNi,Zn) thin films and determined the decrease of Tc and the increase of residual resistivity due to Cu-site substitution, taking into account the CuO-chain contributions to the total conductivity. Although Zn suppresses Tc stronger than Ni by a factor of 2.3 the increase of resistivity differs only slightly. Furthermore the observed resistivities are too high to be explained within scattering from point-like defects. To reconcile these contradictions, we assumed finite size scattering potentials, which lead to scattering phase shifts ?l of higher angular momebtum l > 0. Tc-suppression is discussed qalitatively within this picture.