Member Selection for Prompt for Department determines which Generation appears in Report

Content

We have a request to show the Level 0 members when the top parent is chosen otherwise show just the member selected. I have attempted using an IfThen() statement but just not getting it to work when selecting a member that is not the top parent. This member is on a row. I've attached a document showing the hierarchy layout we are using. 

In the attachment, circle 1 is the top parent that should show the Level 0 members when selected and circle 2 is a good example of selecting just the one member and wanting to show just that member in the report.