Was able to get in touch with someone that was able to help.
Unfortunately, the default coordinate system of a part is not permitted as an option once you are in an assembly level.
What I needed to do was just define a new coordinate system at the part level:
Insert>Reference Geometry>coordinate system
THEN in order to maintain a porosity normal to the face I wanted, I had to define each porous part as a separate porous media rather than all under one definition.