Someone posted images of the Chicago Auto Show on EcoModder. They posted up an engine bay shot of the 2018 Mirage. It seems to be missing the air guide that was specifically added to the 2017 model to improve fuel economy.
Here is the 2018 from the auto show.
Here is the dealer training image that specifically tells why it was added.
Could it just have been removed for the show? Seems odd, and I do wonder if it was removed for the 2018 model year.