We have some additional info written down in the handbook.
Basically, it will come down to your room and personal preference.
There is no right or wrong and you can easily test it for yourself.
Just disconnect the jumpers between the binding posts and connect the speaker using the lower connection.
With that, the speaker will run in direct-firing mode, like a normal bookshelf speaker without the side drivers.
In the default TriAxial mode, the side drivers are wired out of phase and they create a bigger bubble of sound, but with the addition of the front-facing drivers. So you still have lots of direct sound and not a diffuse mess.
I personally like this setup and especially in smaller rooms, sitting right against the back wall and with close proximity to the speaker.
They will give you the sense of a much bigger sound than a normal bookshelf speaker would.
A normal direct firing speaker will always need the right distance and angle to develop some sense of sound stage.
The same principles as with your front speakers apply.