Have created any other slots? Because whether you flash something in the slot or not, if it's created than it's taking up space. When you create a slot it partition's a part of your internal memory for that slot. You start off with 8gb than use 2-4gb per slot depending on the size you choose. Not exact numbers, I'm rounding stock slot doesn't use that space but what you save to your internal sd card does use that space. So it could be ROM slots or saved data that's taking up space on your internal storage
Thanks for the feedback.
I realized that I had saved some tunes to the device memory through google music. Even after deleting that, though - on device memory still only showed 4gb remaining on stock rooted JB...weird. Went through and deleted a bunch of stuff, too. Nevertheless, I'm amidst the install on jellywiz and allocated 2gb to this slot. I'm assuming that's ok.