Hi,
I’m sorry, my bad, I completely forgot about the fact that the search uses the post excerpt as the primary description field, and the content as the secondary by default.
Try changing the primary and secondary description fields as following: http://i.imgur.com/p0qVMUb.png
So the post content becomes the primary source.
Also, I see you have some longer articles, but all of them mostly contain simple text. I believe you can safely increase the depth value to 500000 (half million) characters, so it covers everything possible: http://i.imgur.com/g2H2o0d.png
After these changes you should definitely start seeing the highlighted texts as expected 🙂 I hope this helps!