Is it possible to preview uGUI in the editor for high dpi devices or retina resolution devices, such as the iPhone 5S and iPhone 6?
These are at double the resolution and even if everythings looks right in the editor, this is not the case on-device, with everything scaled down by 2.
I don’t think it is supported currently since when in play mode unity just uses the resolution and screen density of your monitor to display the play mode window.
You have to make a build and test it on device itself. Although it would be great if we could also set the screen density for play mode window.