It's all about the acuity (and how the docs medicate them...but we won't go there). On days when we had that many staff, it was because SEVERAL patients were on 3:1, 2:1 ratio, 1:1, and so on. Yes, some were so severe they had to have 3 staff following them around just for them. Then you have to have male and female, etc etc. Trust me, we weren't standing around idle...too busy trying to protect ourselves from flying chairs, computers, ceiling parts, and broken electronics! And writing it all up to the risk mgt later. These were adolescents, most adults are not as volatile.
I've worked adult places, other facility, where the patients have responsibility and accountability, and it's more like 35 pt to 1 nurse and 2 or 3 MHA. The patients don't pull any nonsense and violence & destruction was rare b/c if they did they went straight to jail with criminal charges on them. I remember one time a nurse got slapped in the face there, by a patient, and quit instantly--that was considered high violence to them!