Ansys ACP(Pre): Apply one "oriented selection set" to two surfaces, with opposing normals?

Hello,

I am new to Ansys ACP and am trying to set the element normals of a box spar using an oriented selection set. I'd like the normal direction of the top surface to point in the positive z of the rosette, and the bottom surface to point in the negative z of the rosette (so the part is being built up inward).

I'd like to do it in one oriented selection set, but when I do that both surface normals point in the positive z of the rosette. Is it possible to do it in one, or will I have to create an oriented selection set for the top surface and another for the bottom?

Thank you