Hello @Rui.Zhang03,
It is okay to only provide the bounding box information at the part level – if you’d rather not convert the assembly in order to better manage hardware resources such as RAM.
For clarity, the part in question in this case is the one referenced with <ExternalModel/> as stated in point #10 in our docs.
If you find that using cutoff scale is not working as expected, our recommendation would be to create a support ticket in our portal. As it is likely that we will need the source CAD file to do a more thorough investigation.
Thanks,
Tino