You could delete your Layout.

And then from right click on Layout, in the toolkit and run the Layout wizard.
If instant-swap is enabled, the wizard should make the smaller windows the same render resolution as the main window, which will allow accurate mouse broadcasting.

Another approach, is to run all your regions at full size, and stack them.
Then use video feeds to show the portions of the slave windows that you want.
I've not gone this approach yet, but there are lots of screenshots of people who have and some of those look quite neat.