Set different rootfs sizes

Ok, I know its an unusual question, but hear me out. I’ve got a BeagleBone Black with a Debian image thats already customized and performs its duties. I wanted to add a Mender component to this utilizing the dual copy strategy. The problem is that my base, golden image is about 300mb too large for the installation and it has to be on the 4gb emmc as I cant use an sd card.

I want to test something out and for that to work, I need to one rootfs to be say 2.5gb and the other rootfs to be 400mb. Looked through the variables and the settings and what not, but I could not find any instructions. Does anyone have any suggestions? Is it even possible?

with respects to the 2.5GB rootfs size, have you gone the usual process of ensuring that man pages, multiple kernels, apt package cache, swap file, etc are not part of your golden image to reduce the size of your rootfs installation?