Hi @SwingeyP ,
Not a problem at all, i’ll see if I can help you out here 
Unfortunately, sub tabs cannot be made into popups.
But it does sound like a cool idea - You could raise an idea in the Ideas Portal so that we could consider allowing sub tabs to be popup pages.
If you want to utilise popup pages, it’s done a little bit differently as popup pages are not tied to your navigation hierarchy. You would need to create a Page component and set the utilisation to Popup page.
Then, wherever you want to display your popup (e.g. inside of a page, your viewport nuggets, etc) you would use the Popup page element to display a button/link to open the popup page.
Just make sure the base object of the popup page matches the context in which you use it in.
For example, if your page object is User and you want to edit that same record in the popup page, you would ensure the popup page has a page object of User as well.
Hope this helps