I also started using redshift (linux equiv to flux) several years ago and gradually used it more, even during the day, as I also found it seemed to help mitigate migraines at least to some extent and it just generally reduced my eye fatigue.
/usr/bin/redshift -O 3500 -b 0.7
It instantly makes the screen easier to look at, no matter the lighting conditions. I also have a command to revert to normal color: /usr/bin/redshift -O 6500 -b 1.0
Curiously, "redshift -O 2700 -b 0.7" is less comfortable than 3500K because it's too yellow. I think what bothers me about screens is heavy saturation in any color.