Anfisa, fiction books I tried to read range from '5 words I didn't know per a book, mostly adjectives' to 'every 3d phrase I can't understand'. In other words, books, they differ:) The bad news is that
1. when I understand a lot I rarely look into the dictionary. I'm following the story, I deduce some things from the context....And just skip unnecessary words:( So, my language isn't getting better with the easy reading.
2. On the contrary, when I do look for the word in the dictionary - I often look for the same word 100th time in my life, and I still don't remember this word! There're ways to overcome this. 2.1 draw a dot against the word you're looking for on the margins of your (paper) dictionary. When there're 100 dots against the same word, then something is wrong))))
2.2 Use this word in order to remember it.
So, I don't sure that reading alone (without listening and speaking) has great language improving potential for adults at the level where you read 'fluently' enough.
Happily you aren't that good) I can't answer your question directly, but that's what I know on the subject. And yes, I agree with Barrett.