This should not be necessary. I have never kept PST files on drive C.
It is probably just remembering where you were last time you used that function.
When you add a PST file manually, it adds a prefix to the name, something like X1 Profile ABCD1234 (past filename).
Where are you doing this? You can't add empty Outlook accounts on a drive.
I sense something jumbled in what you are doing in Outlook.
Here's how I manage PST files that are not a part of my day-to-day Outlook operation.
I go to Windows Mail and create a new Profile. SA profile has nothing to do with drives, or with PST files. At least, not at this stage.
How you create a profile depends on your version of Windows. Mail is a part of the Control Panel.
I create a profile and ignore Windows when it invites me to associate an email account with that profile. You have to press Cancel to get to this prompt.
When I have got the new profile, in Mail Setup I go to the Data Files... bit and add the PST files that are not already associated with my main mail profile.
X1 then detects the name of my extra profile and adds all of those PST files without prompting.
Then you can go into X1 and check that it has found all the stuff that you added in the Profile.
Before you do anything, you should invest8igate your main Profile in Outlook. The work out how to see what databases (PST files) it is using. X1 will see all of these. If you find that it has added PST files that you sense it is not indexing, then something else is happening.
Once again, this is getting confusing because you have thrown a query about X1 6.7 into a long running discussion about Windows 8. Your scenario is unlike that in the first question. Nor do we know what version of Windows you run. So I am really just guessing here in the basis of past experience.