Basically that's what we do.. in other words, an obvious greater than 50% on area for the .45 is good. We're a little bit more forgiving for the .22s though. If they hit the edge, we usually call it.
Keep in mind the double and triple areas are about 1/8th of an inch thick, and a .45 230gr ACP hole is like 1/2" thick. It's a pretty darn small target!
It's rather funny how other folks got into this silly game at our range. It used to be just us and another couple we know. A couple guys shooting on their own wondered what the heck we were doing with our targets so close, and just thought us either crazy or complete handgun newbies. Now one of those guys and his wife is into it, and got another few folks he knows into it too. We're now 12 regulars who do this a couple times each month, with almost 20 people involved in total. It's pretty fun and competitive with some guys even taking it too seriously at times!