Five numbers decide whether a page is legible to a retrieval system. Here is what each one means when it is bad.
Chunks that never reach the index
A retrieval system reads a fixed number of passages from a page and ignores the rest, so anything below that cut is invisible no matter how good it is. Vectorscope applies the same cap the product applies and names the passages that fell outside it.
If your answer, your price, your differentiator or your FAQ sits below the cut, the fix is not more words. It is moving that passage up, or splitting the page so it has a passage budget of its own.
The extraction ratio
The extraction ratio is how much of the page turned into readable text — a low one means most of what you shipped was navigation, boilerplate or markup that no model will ever see. A long page with a low ratio is a short page as far as retrieval is concerned.
Common causes, in the order we see them: text rendered only by JavaScript, an article wrapped in so much chrome that the body is a minority of the document, and images carrying words that exist nowhere in the HTML.
Groups, and what a tight group means
Groups are passages the embedding thinks are about the same thing, and one enormous group usually means the page says one thing many times. That reads as thin to a retriever even when it reads as thorough to an editor.
Several small groups with one passage each is the opposite problem: a page that changes subject constantly gives a retriever nothing complete to quote.
The passage a question actually retrieves
Asking the page a question returns the passages that answer it, ranked, using only that page — which is the closest thing to watching a model decide what your page is for. If the returned passage is not the one you would have chosen, the page is not organised the way you think it is.
This is also the fastest way to test a heading rewrite: change the heading, run the page again, ask the same question.