What the centre channel carries
The centre anchors dialogue and a large portion of front-stage effects to the image. In movie playback it often works harder than either left or right channel.
Behind the screen is ideal
An acoustically transparent screen lets the centre speaker sit at the visual centre of the image rather than below it. This is one of the strongest arguments for cinema-style screen construction.
Horizontal speakers are not automatically wrong
A horizontal cabinet can be excellent if its driver geometry is engineered for that orientation. The problem is not “horizontal” itself; it is uncontrolled off-axis interference across a wide seating area.
Early reflections mask dialogue
Hard surfaces near the centre speaker can create strong early reflections that reduce clarity. The screen wall and nearby floor/ceiling surfaces should be included in the acoustic design.
Do not fix poor intelligibility with level alone
Turning the centre channel up can make dialogue louder without making it cleaner. Directivity, placement, room decay and equalisation must be addressed first.