I wrote about a billion articles on Admission Control by now: Search for "admission control" - Yellow Bricks
Anyway, first of all... Admission Control is not about "resources used" but rather "resource reserved". When you do not have a reservation for CPU or memory then default values are used. So even when you set "admission control" to 60% it could still be that when 1 host fail ALL resources are actively used. The VMs can always demand more than what is statically reserved for them right.
I would just monitor DRS resources and ensure you aren't running at over 60% with two nodes in your cluster. I guess the question is, how much of a performance hit can you take when there is hardware outage.