You can actually. MP follows the display rules set down by each PC.

For instance on my desk I have

Comp1 Comp2 Comp3

Each computer has two monitors but Comp 1 has one stacked on top of the other. So it goes:

Mon2
Mon1 Mon 3 Mon 4 Mon5 Mon6

To do that I just went into the display settings and set the Mon1 to the 1 spot on that machine. Then I placed 2 on top of it still in the display settings. You could always get the settings you wanted with machine positioning in the advanced grid through Multi Pro. It is under the Config tab. Set Comp 1 and 2 to be on top of 3. Then just make the 3 machine monitors row out. The only thing you would have to contend with possibly is a small jump in the cursor as you moved to the third machine.

For that connection try checking the "look up IP address each time" box in the configure settings from the secondary machines menu.

What you have to know about multiplicity is that it does not think in monitors. It thinks in computers. Once it gets to another computer it respects the settings you have in your display settings menu.

So what that last listing should be is:

Secondary 1 = [1]
Secondary 2 = [2]
Primary = [P]

[1][2]
[P]

or [1][2]
        [P]

This can all be done through the grid function in the pro version of the software. However the monitors are not going to line up the way you would want to in that scenario. If you wanted to get a "quad" set up it would be much easier to have two computers running two monitors each

[1][1]
[2][2]

By designating that they are just on top of each other and they have mirrored display settings you would get the desired effect.