Self-consistent field theory is used to study the effect of asymmetry between A and B statistical segment lengths on interfacial properties and phase behavior in ternary mixtures of AB diblock co-polymers, A homopolymers, and B homopolymers. We consider systems with volumetrically symmetric homopolymers and co-polymer, in which a difference between A and B statistical segment length is the only source of asymmetry between A and B monomers. The sign of the spontaneous curvature of monolayer interfaces between A- and B-rich homopolymer domains is shown to depend on the ratio of co-polymer to homopolymer chain lengths: Interfaces preferentially curve toward the component with a higher statistical segment length when the homopolymer lengths are greater than or comparable to the copolymer length (as also found in diblock co-polymer melts) but curve away from this component when the homopolymers are much shorter than the co-polymer.