I agree with your point, but it is very common for clinical staff to work 12 hour shifts and do 3 or 4 per week.

That's easy, obviously the patients will be moved to a 4-day-week as well, and adjust their recuperation accordingly.

Which is, of course, why a trial of self selecting companies mostly in the knowledge work sector dropping down to 0.8FTE doesn't tell very much about the rest of the world

Basically jobs where the person is providing real time services, whether flipping burgers or providing technical support, etc.