I might need more information to totally answer your question, but yes you can have multiple metrics and comparisons in a single custom narrative. The only limitation you could run into is there is a limit to the number of categories you can add to a single insight visual.
It’s been awhile since we last heard from you on this thread; are you still working on this or were you able to find a work around to implement for your case?
Have you tried building out a calc. field to rank the container volume’s CU and use that in your narrative?
If we do not hear back within the next 3 business days, I’ll close out this topic.