Do you have a sample workbook to show what you are asking about? From reading this, I am not sure if this is in reference to a nested table calculation or something else but seeing a workbook, we could figure it out.
The Default Table Calculation is what it says - a place to set the default compute using of the table calculation when the calculation is brought into the view. The fields available in this setting are only those from the primary, and due to the way table calculations work (they are after aggregations and computed in Tableau) those fields must be in used in the view as dimensions for the table calculation to work.
As Patrick noted it sounds like you are trying to nest calculations. We can nest table calculations and that requires the viz to have the proper dimensions to get all of the underlying aggregations to work and then the proper compute using settings on each of our calculations. Another way we can nest calculations is to take advantage of Level of Detail (LOD) expressions, see Level of Detail (LOD) Expressions | Drawing with Numbers for a number of useful links.
BTW in my training classes I don't actually recommend for my students to use the Default Table Calculation setting. The major reason why is that if we bring a table calc w/defaults set into a view w/out those dimensions in the view then we get a red pill and the view stops updating and then we need to open up the table calc to figure out what defaults it is expecting and then bring those dimensions into the view which might break our other calculations. Instead I recommend using a comment in the calc to indicate what the expected compute using is so users can explicitly set it.