The DTD view for End of Period Headcount includes a column for Average Headcount and vice versa.
SuccessFactors Workforce Analytics - Drill To Detail
Reproducing the Issue
Open End of Period Headcount and click any number in a table to open DTD. View the available columns.
Average Headcount and EOP Headcount are sourced from the same object table, which has a single DTD config attached. Columns for both measures have to be included in the same set of columns for the Workforce object.
To re-implement one of these measures in a separate object (for the sake of separate DTD config or otherwise) would be a major piece of development potentially affecting all Workforce measures. It is not recommended.
It is possible to hide the column for yourself and other users by creating a custom DTD view. The controls for this are at the top of any DTD display. You could name a view after each measure so people know which one to use.
KBA , LOD-SF-WFA , Workforce Analytics & Planning , Problem