On the basis of ab initio calculations we study the interfacial magnetoelectric effect in a prototypical biferroic Fe_L/XO₂/BaO/BaTiO₃(001) (X = Ti, V, Co), with an Fe thickness L ≤ 2 monolayers. We anticipate that the use of n-type perovskite termination instead of nominally neutral TiO₂ may enhance magnetoelectricity in the system when its magnetization is robustly changed by substrate-polarization reversal.