It also depends on what mode the ME1 is in. They don’t have to follow the same layout you have in the IO section they can reprogram the ME to have what they want from whatever you make available in the IO screen(40 channels to choose from).
In the default mode the ME 1 will assign the first 16 channels in the IO to the keys. but you can also assign groups on the ME and have multiple inputs under one key. For more info see the ME manual starting at pg 21-24.
As for the IO screen set ME1 mode then choose an output and at the bottom assign what goes there, usually ‘input direct out’ then the channel number in start then hit apply.