My Help "Knowledge" Search Results - Knowledge Article Excerpt Display Logic and Options

We are noticing that when users search in My Help for knowledge, the articles and attachments that appear have a preview/excerpt from the articles and files. Firstly, we wanted to understand the logic that is used for these excerpts. It seems that sometimes the excerpt displayed is quite large/long compared to others, regardless of the amount of content in the articles. Is there any way to control of modify the behavior that the excerpts follow?

Also, we see some weird inconsistency where two articles have a similar sentence in the very beginning of the article. The problem is, one article excerpt shows this first sentence, but the other article does not show this sentence. It seems strange to us: