Considerable work has focused on the use of epitaxial strain to engineer domain structures in ferroic materials. Here, we revisit the observed reduction of domain variants in rhombohedral BiFeO3 films on rare-earth scandate substrates. Prior work has attributed the reduction of domain variants to anisotropic in-plane strain, but our findings suggest that the monoclinic distortion of the substrate, resulting from oxygen octahedral rotation, is the driving force for variant selection. We study epitaxial BiFeO 3/DyScO3 (110)O heterostructures with and without ultrathin, cubic SrTiO3 buffer layers as a means to isolate the effect of "symmetry mismatch" on the domain formation. Two-variant stripe domains are observed in films grown directly on DyScO3, while four-variant domains are observed in films grown on SrTiO3-buffered DyScO3 when the buffer layer is >2nm thick. This work provides insights into the role of the substrate - beyond just lattice mismatch - in manipulating and controlling domain structure evolution in materials.