In my opinion, the system has failed.
The problem is that the note below the answer isn’t visible. At all. For instance, I completely missed it on this question and only noticed it after it was mentioned in a comment – and after I actively looked for it, still overlooking it the first time.
In my opinion, the solution should be very easy, and I would be interested if anybody finds it controversial:
Put the banner above the question / answer.
A common objection to editing the post was that “it’s intrusive”. But that’s the purpose! It should be intrusive, it should be noticed. At the moment, I don’t believe that the majority of users notice the banners on the majority of posts.
The banners currently also fail at a basic, very useful function:
The banner's boilerplate text should or must include a hyperlink to a relevant/helpful/informative FAQ page.
This should be fixed as well.
Notice: This is a UX problem. Developing a proper design for the banner might mitigate the problem. But I still feel (strongly) that changing the layout rather than the design is a better solution. Put the banner above the related post.