For 5.1.2, Dolby recommends placing the surround speakers behind the listening position. Why? Wouldn't it be better to have them next to the listening position as recommended in a 7.1 setup? :
Dolby Atmos® Home Theater Installation Guidelines
In-wall and ceiling speaker placement and installation
Dolby Atmos 5.1.2, Height Speaker Placement | AVS Forum
Surround Sound Base Layer Speaker Placement - YouTube
Atmos/DTS:X height channel physical placement in an old house... | Audio Science Review (ASR) Forum
11.1.8 Mounted / Overhead Speaker Setup - Dolby
How Do I Position Loudspeakers for My Home Theater System?
Dolby Atmos® Home Theater Installation Guidelines
Dolby Atmos Speaker Placement - Modus VR
2.1 To 11.1.8 What Does It All Mean? - A Refresher - From Vinyl To Plastic