My numbers are based around super-hard-to-argue-against standard employment law for other professions where I live. If you work as a waiter or a shop assistant that's the sort of overtime deal you get automatically.
When you push that minimum legally required remuneration to its obvious extension if your boss is asking you to be on duty 24x7, it's difficult for them to argue a reasonable case _down_ from having to pay you 8 times as much money.
The primary aim of that line of reasoning is to point out "if you need my job covered 24x7, employing and paying another four people with my skills to make sure it's covered for the 130 hours a week I'm not in the office is a more reasonable and less expensive way of doing it than trying to make it all my problem."
Quite often, in my experience, it's because the boss suddenly has their first customer ever suddenly demanding it, and they've not done the maths already and been immediately able to tell the customer "Sure. That'll cost you about ten times as much as a weekday business hours only support. When would you like us to start billing that? I'll need that in writing, of course."
I would be giving up time with family, excercise (my health), and my other goals, so I don’t see how a simple 2x would even begin to cover the loss of those.