If you look at the stock wallpapers, the perspective stays the same when you 3D touch and the animation plays in reverse when you release.
Custom wallpapers are different. Firstly, as soon as you touch the image blows up by about 10% cutting off the edges of the image, which is really bad especially considering that the display is already so narrow. Secondly, upon release, it simply fades back to the original rather than playing in reverse. For some wallpapers I could see how that might be what you want, but for me this isn't idea and I would like to keep the reversal.
Does anyone know how to create a custom wallpaper that does not "zoom in" and plays in reverse upon release?