Hi James,
Happy to hear you are beginning your TBM journey. This likely has to do with your object identifier set for each of your modeled objects. I've linked 2 useful articles below that might be helpful for you.
Amanda does a great job explaining what an object identifier is and why it is important:
https://community.apptio.com/communities/community-home/librarydocuments/viewdocument?DocumentKey=5ed44038-63b2-4ca0-a0ae-fa7b9568d4a8&CommunityKey=425255f0-2344-4925-89f0-f0eced22345e&tab=librarydocuments
Best practices for object identifiers:
https://community.apptio.com/viewdocument/best-practices-variable-granularit?CommunityKey=3ff74a27-8291-48d0-ba5a-403be94d07b8&tab=librarydocuments
Thanks,
Joe
#ApptioforAll