My app is optimized for iPhone 6/6+ using the appropriate launch screen images. I did notice an interesting behavior though. I am no longer supporting non-retina screens so I deleted an image.png for which I had included in my bundle an image@2x.png but not an image@3x.png. I build and ran on an iPhone 6, expected behavior.
I build and ran on an iPhone 6+ and the image was missing completely. I ran again on 6+ simulator and the image showed. I added image@3x.png and back to expected behavior on both simulator and device. I don't recall it being this way with image to image@2x, for example if i had image it would just scale up to 2x if I did not include an image@2x.
For the sake of experiment I deleted image@3x.png and added back image.png, ran on device, image appears. Does this mean that images are being scaled from 1x to 3x? Seems it would make more sense to me to scale the 2x image to 3x?