Without knowing zram details, I figured there would be a limit to how much is useful to allocate
Why would Jolla ship an underpowered configuration for so long? But indeed Drop swap for zram on Linux | Opensource.com seems to support an idea of < 8G RAM systems having 95% zram allocation 
I did initially also double zram, but it also ran out fairly quickly. Perhaps increasing both zram and adding a swapfile is the secret sauce? Going to test this next.