What I am suggesting here- cams mounted high inside looking somewhat downward- is the very thing I do with my side cams, so I know what they can do. He apparently doesn't have any experience with side cams at all but thinks he has expertise on the subject. Due to the length of my van I don't have full side coverage, but where my cams do cover I can see someones hands at their waist level within about a foot of my van and that will almost certainly show if a key is in their hand, along with the physical action of them reaching towards my van and dragging their hand (and likely still with the key my cams just saw in it) alongside of it, which they would hardly have any other reason for doing such an action. Only someone who knew my cam system and it's limitations could key my van unseen, and that information is not apparent from outside my van even if someone did notice my cams- which most people don't. And other folks here are showing similar findings to mine. So I don't believe my advice to be bad, and I can't see nor have I been shown how any other practical arrangement could do any better with only a pair of 2-channel cams which still retaining good usage for driving. If you get right down to it, you would probably need close to a dozen cams to give 100% coverage of a car's painted areas to catch someone keying it regardless of how they went about it, and that amount of cost and effort almost reaches to being absurd. But it's there if you want it, and you're free to be as absurd as you like as is evidenced by Honest Review, who is now on the very short list of people here who I am done with because they are simply not worth wasting any effort on.
And to those who might care, do know that the OP and I are conversing via PM now, so he's not been abandoned.
Phil