I have the RadTech Sleevz for the iPad Mini, and although it takes a bit of doing, a bit of wrestling the first few times, it WILL indeed fit the Mini plus the Smart Cover. I doubt that it would fit with anything else on the back. The fit IS snug. The first time, I put the iPad Mini in there by itself, and that works very well. Next, I slowly maneuvered the Smart Cover in there and then had a small piece hanging out, but the basic thing was in there. Next I worked with inserting the Mini with the Smart Cover on -- it takes some doing but each time one does it, that helps to stretch out the fabric a bit and makes it a little easier. Actually, what I had been doing until the new iPad Mini-sized one arrived was to use my larger one that I have for the regular-sized iPad, slipping the Mini into it, folding it over at the top and sticking it into my bag. That works well for protecting the Mini while in a bag and also makes it pretty quick to remove/insert back into the Sleevz as needed. This way since Day One when leaving the house my Mini has had protection on the back. Once I get the smaller Sleevz stretched a bit, that will be the one which goes on the Mini when it leaves the house.
Instructions from the RadTech website:
To put on: Grasp the RadSleevz case at one of the ends, with your left thumb inside the cavity, and let the case hang vertically from your thumb. With your right hand, grasp your iPad in the center - back edge toward your palm. Drop the end of the reader into the dependent end of the RadSleevz. Pull the upper end of the RadSleevz (left hand) over the top edge of the reader, and pull on as far as possible. While still holding the iPad in the center, slide the bottom, then the top of the RadSleevz onto the device.
To remove: Grasp the iPad in the center. Pinch the bottom, center of the RadSleevz and slide straight off.