Logic Pro X Atmos and Speaker Channels


I'm taking my first experimental steps into exploring Logic's Atmos features. At this stage I have cobbled together a 7.1.2 system and got it all calibrated with my SPL meter and tape measure.

So not being on Monterey yet which the latest versions can decode Atmos streams to multiple speakers (yippie) the only experimental Atmos content I can listen to is the Lil Nas X - Montero Logic Pro Demo.

After listening and being blown away by all the sounds flying around I realised that my 2 height speakers were not receiving any audio despite audio being sent to those channels so really what I was hearing was the 7.1 without the .2 and this is my question.

I have all the right outputs assigned in the audio IO section of logic and if I turn off the Atmos plugin on the master strip I get all 7.1.2 speakers receiving sound as expected. Turn on the Atmos plugin on the master and the height channels fail to receive sound despite I can see in the multi channel level meter on the master strip that sound is being sent to those height channels.

Any thoughts here folks?

Kind regards