Nighthawk Mesh DHCP issue

So I am having an issue with DHCP reservations.

Currently it will not allow me to assign 2 MAC addresses to the same IP address.  I currently have that setup on the Apple Airport Extreme that I am migrating from, as well as my previous Linksys router. 

I have this setup for devices that have both a wired and wireless connection in the event that one fails when the other connection takes over the device has the same static IP address for streaming of files.  (IE Xbox one or Amazon Fire TV which only have one connection active at a time.)   

Does anyone know of a setting that I am missing that will allow me to set this up? 

Also side rand- the 15 character limit is stupid.