I know the Mini and the Mini GT have identical storage space. I'm not sure about the Elite. Storage space is one of the things I like least about the Mini GT I have. I have found it's easier to put something in the storage space from the side than from the back, and once I learned that trick, I can fit a lot more. The hole for putting things in from the back is too small, but from the side, you can pull down the elastic and get a pretty good-sized diaper bag in there. I use the Thirty One bag Organizing Utility Tote (Approx. 15.5" W x 10.25" H x 6.5" D) as my diaper bag and can squish it into the storage space with a bit left over. My bag is about 3/4 full so can be squished a bit.
Other than storage, I really do love the stroller.