You're right, I meant water+flour+starter denominator. Didn't figure salt would matter enough.
My math brain wants everything as a percentage of a whole, but I see how it's simpler the way it is. Especially since the starter also has some relatively unknown amount of water and flour inside itself.
Once you're going for consistent loaves eg selling them to people who expect them to be the same every day, you do have to factor in hydration of the starter. Usually you keep it the same as the dough for simplicity but there are reasons why it might make sense for them to be different.
My math brain wants everything as a percentage of a whole, but I see how it's simpler the way it is. Especially since the starter also has some relatively unknown amount of water and flour inside itself.