Thank you for contacting support about this problem!
If I understand correctly, I would first recommend to ensure that you have a relationship set up with any apps in other the workspaces, you may need to request access from the admin. This should allow you to choose those fields for your calculations.
Beyond, this I would recommend to post your question in our Calculations forum here:
I may have it wrong, but it seems a reasonable assumption to me.
Podio - Dana