From memory when doing this before I needed to rotate in blender 90 degrees so the face was facing towards the floor, probably because I couldn’t be bothered to figure out the export/import orientation, also once I had the mesh in the same state as you if you duplicate the original face mesh and then assign that to the MH blueprint then open that mesh and at the top of the screen in the import options select reimport base mesh as new file, select your new mesh and import and this should fix the issue you’re having.