Just curious, but why would you expect lower salary for essentially the same time being worked?
They're misunderstanding the meaning of the phrase.
Real //coverage// requires shifts of multiple people for the same job. "Being reachable", used to involve special extra pay just for the option of being called in (actual pay).
I keep trying to push the boundaries outwards in negotiations though, trying to find their breaking points. Often, it surprises me how much I'm able to get away with.
The samizdat of our times might just be about _actually_ working while wading through seas full of these creatures.