synergy

Please ignore the ass behind the CyKo, Marnie. I'm sure your setup is much more advanced than they can even comprehend. The config you've already come up with shows you definitely know what you're trying to do. ;-)

The fact that PC1's monitors aren't a square is definitely going to make things difficult. Unfortunately, I have no way to test what I'm about to suggest, but give this a shot and see what happens.

Since PC1 is essentially 3 monitors across, split the top edge into three pieces of 33% each. Don't specify 0-33% since it technically goes nowhere, but 34-66% goes to PC2, and 67-100% goes to PC3. Of course, you also need the opposite links to tell Synergy how to come back. With this setup, I'm guessing there will be a sort of "invisible gap" that the mouse will have to go through between PC1:M2 and PC2:M2, and PC1:M3 and PC3:M1, but the movement should be more logical if it does work.

If you wanted, you could even do essentially the same for the left of PC1 and split it up. Make going to the Laptop be the bottom 50% (50-100%) of the left edge. That way, you'll more logically go just from PC1:M1 to Laptop.

Please let me know how this turns out. I can only wish I had enough PCs and monitors to test your setup. :-)