I don't have ATMOS but if I did, I'd experiment with orientations like the ones I show at the link below.

https://drive.google.com/open?id=1--Wv1h6Yf2KEJPQV8lNXn5hvY31K02tK


House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated