Getting launch image from xcassets file has wrong size [duplicate]
I believe that the correct launch image is loaded automatically at startup. It is not meant to be pulled from xcassets during runtime. Since it is at runtime, you will have to do your own check for which device is being used, as the image catalog is only setup to pull retina vs. non-retina using the @2x postfix (not the size of the device).
You can use this post to determine which device is being used and load the correct image by name.