The url you'd see on the game's page is this:
If you remove the "boxart_160h", you get the following:
Which give you the above HQ box.
A recent example of Project X Zone:
The url on the page:
Now remove the "_160h", you get this:
Which again gives you the above box.
Not all will lead you to jumbo boxes, I tried it with Luigi's Mansion GC and only got a tiny one...
So in a surprise turn of events, IGN's now home to very HQ boxes that put Amazon and others to shame, try it if you're looking for a great box!