When you have knowledge distributed in markdown files; finding them puts the path/filename into context as well as some indication of document size. (If its on line 1200 or line 20). This is extremely valuable for picking what ought to be focused on next.
RAG on the other hand creates the hardest challenge for these models. It instead puts 5 ideas with the highest similarity into the context in full.
Its the difference between having to remember a set of numbers when in a crowd that's talking about stuff, and having to remember them when the crowd is shouting out random numbers. The similarity in the task makes things harder. SoTA models work despite this, but its extra-gambling while you're already gambling.