Do you use multiple levels? Do you see also your text ‘Department 1’ (not in your index) multiple times in your print preview? If you see this department multiple times in your report, your index use this text in display also multiple times your ‘Department 1’ value.
I’m not sure if this is possible. Normally it showed you all the items as many times you see it as header in your document. Normally is your level only showed once. This is different if you use nested levels. Then you can have something like:
Then you have to set Region as level 1 and Department as Level 2 in your table of content.