My experience is that HK pistols are more like #3 out of the factory. The dot is actually a little higher on the post than what is shown in your diagram, so it isn't exactly like that, but it is "put the dot on the button". HK P7 PSP, P7M8 and P7M13 (what I mainly shoot) are definitely all like this, and I believe P2000 and USP are like this as well. (My P2000 is factory, and I'm quite certain is like this. My USP is .40 and has Trijicon's though, which are lower, and I think it gives a bit more of a 6 O'clock/#1).
GLOCK with Trijicon night sights is #1, as are a LOT of other guns. It wouldn't surprise me if the Ruger is like this. My girlfriend had one of those years ago, but I can't remember how the sights held.
If you are shooting at a circle-type target, probably start with #1 and work from there. You need to be able to shoot well enough to know what it is actually sighted in for though, and that won't come right away, but I think you have it right. HK for generations have been "put the dot on the button".