I am underserving you because I just can't experiment with that setup (even if I were in the office it would be a challenge). And frankly, it's driving me a little nuts trying to visualize how I could make it work and still feel natural - the mouse movement.
Remember, MP cares what is the entry and exit to transition, it does not pay attention to how you have your monitors arranged (God will grant me that someday). So if it sees that it has reached the end monitor you have in Windows, it transitions.
With that, you may have to snake your way to certain monitors (something you have likely learned already). What also plays a role is what you have set as your 'Main' monitor in Windows for each PC.
I want you to turn this on and go down on PC1 Mon1 and see where the mouse comes out:

Ensuring that your grid has your Secondary above your Primary:
There are also hotkeys to get you to any monitor if that is a solution at all for you.
Sean Drohan
Stardock Support Manager