Outlook OST file

I have MS Outlook and my mailbox is "Administrator" in Exchange server. I have added to Outlook a Resource Mailbox as shown as "Conference Room" and also added another user mailbox as shown as "Test Test".

I wanted to check how many OST files get created, and I found just one Outlook Data file(OST) for Administrator mailbox , even when I enabled "Use Cached Exchange Mode" for all 3 mailboxes .
Now I wonder if all 3 of them use the same OST file, which I doubt it.

Any idea?

Thanks