When surround sound started being a thing, it was originally intended and mixed for "ambiance", hence it didn't really matter if they were higher/farther/dipole/diffused etc. However, modern movies use aggressive discrete mixes that treat all channels as full range so you want to consider them as real equal speakers like your front stage (toed in, ear height etc).
Same thing with Atmos. The spec is actually for full range for all channels and 90hz if bass managed, including ceilings/heights. Common misconception is that they get small effects for ambiance and people stick little speakers crossed at 150hz or whatever. The downward vs aimed is more for your room coverage. If you have a large room with multiple seats, you want to just fire them straight down and use high dispersion. But if you have a normal living room or small room setup with a money seat, you want to AIM them towards MLP, no different than toeing in the front L and R etc.
