Posted in ArcGIS Online space originally and was suggested posting in 3D space.
I did a little test on back face culling with a created box of which all outer faces were facing inside and inner faces were facing outside (see FaceCullingPro.PNG), and it seemed that when a slpk was created, even though the back face culling setting was kept, it displayed as if the normal was flipped (see FaceCulling_slpk.PNG).
Does anyone know why this is happening? I am relatively new to creating 3d content in ArcGIS. Much appreciated it if somebody could shed some lights on this. Thanks!