That's by design and a problem that is especially globally discussed by Atmos experts, when it comes to Atmos Mastering.
That means, it's not only a problem in Studio One.
What Studio One lacks is the ability to create an Object Bed, especially for the very common 7.1.4 speaker layout. This is especially important for realistic room reverbs in setups larger than 7.1.2
Time will tell, how the industry will solve this dilemma.
Dolby's recommendation is to use a 7.1 bed and create 4 static objects for the ceiling in a 7.1.4 setup. But routing such a setup is nearly impossible in Studio One as far as I can tell.
I'm open for tips ;-)
PS: If your question has it's origin in trying to master an Atmos song, have a look at this solution, which creates a pseudo mastering bus:
https://www.hornetplugins.com/plugins/hornet-samp/