That's the problem with the Samsung OEM wireless charging rear cover. It's thicker then the stock battery cover, while it isn't a ton thicker it is thick enough where most cases won't fit anymore.
I have the Spigen Slim Armor, and after I got the Samsung OEM wireless charging cover, I tried to put the Slim Armor case back on and it wouldn't fit. The wireless charging cover was too thick for the case to fit now.
From what I've read, this is a common problem if you decide to go with the Samsung OEM wireless charging cover. There are 3rd party wireless charging receivers (such as the one from Fonesalesman on Amazon via link below) that others have reported working with the stock battery cover, and also work with most cases. However with 3rd party, specific things you need to be concerned about are potentially charging warm, needs to be positioned on pad very specifically, may interfere with NFC, etc.
And all this sucks because I didn't know about it until after I already bought my Samsung OEM wireless charging cover and pad. At least I got them both at 50% off and can resell them as they've never been used. But still an added hassle I wasn't anticipating having to deal with.
I don't understand why Samsung couldn't have either made the stock battery door thicker to match the wireless charging cover, so cases designed for stock GS4 would still fit? Or why Samsung couldn't have simply made the wireless charging cover the same width as the stock cover??