Why is my Logic Pro X only outputing 10 channels instead of 12 in Dolby Atmos mode?

if I go into the audio midi setup and click on configure speakers, all 12 channels work with my sphere audio software. Or it also works fine if a play a Dolby Atmos track in Apple Music. but when I set up logic to read 12 channels, it only shows up 10 channels instead of 12... Maybe it has to do with my audio interface, a Focusrite 18i20 which provide only 10 physical analog outputs... I'm planning on using another interface to have 2 outputs by spdif, to give a total of 12 outputs. Is this a problem with my logic configuration?

[Re-Titled by Moderator]