Device profiles can be used to set your game's resolution for iOS devices. The
r.MobileContentScaleFactor property is relative to the 'nominal iOS resolution' for a device. For example, a Retina iPad
has actual resolution 2048x1536, but nominal resolution 1024x768, so you would use 2.0 to get native resolution there. You can also use fractional values like 1.5 if you want more resolution but not the
full performance hit from running at native resolution.
The iOS device profiles can be seen in
Engine\Config. These categories are set through a plugin system,
with the default plugin being iOSDeviceProfileSelector. The iOS device categories are simply the name of the device.