[LAU] Ardour: the orange mobile squares in monitor track

Thanks to everyone who shared tips on how to use Ardour. I see that up to now I haven't used much of it really and the recent tips on hardware monitoring are great and I'm still experimenting. At the beginning of a new session I've added a hardware monitor track with 4 outputs PCMs 1 to 4. I'm still not doing much with it at the moment and noticed that in the mixer window there's a fader for it along with a space at the bottom containing 4 green dots numbered 0 to 3. When dragging them in the square space the mix would slightly move sideways. That seems useful. But what about the orange squares located at each corner of the space ? They also can be moved but seem to change nothing - what is their purpose ? Cheers.