Reading comprehension is highly "g-loaded", as psychometricians would say. In other words, it depends heavily on IQ. Arthur Jensen (noted IQ researcher) wrote this https://emilkirkegaard.dk/en/wp-content/uploads/The-g-factor... :

"After innumerable factor analyses had clearly established what types of test items are most g loaded, test constructors deliberately composed and selected items so as to maximize the g-ness of their IQ tests. The most g-loaded items are those that involve some form of inductive or deductive reasoning (i.e., Spearman’s “eduction of relations and correlates”), problems that involve spatial visualization, quantitative reasoning, and verbal knowledge and reasoning (such as word meanings, distinctions between related words, antonyms-synonyms, verbal analogies, and reading comprehension)."

In the linked article, look at what level 5 requires:

"Integrate information across multiple dense texts; construct syntheses, ideas or points of view; or evaluate evidence-based arguments."