GPU0 needs more reserved VRAM for Windows, so by placing an 8GB card there, you don't need to worry about this. It is not to say an 8GB card first and the rest 4GB cards will work past 23rd December 2020, it is to say it'll work until then and not stop early.
To test your theory just add in .bat file -benchmark 353. In that epoch dag size is 3.76gb and miner in Windows fail to create dag. Maybe you will need to use Claymore's miner because Phoenix has some bug when you start -benchmark option.
my test in Claymore with IGFX primary gpu:
epoch 353 dag 3.76gb
Windows failed , Ubuntu works
epoch 378 3.95gb
Ubuntu failed