I did not practice RC at all. I took 2 achiever tests and the reading in those practice tests were hard but somehow I pulled an 18 so I figured that's good enough. Then I read the articles on the test and they seemed to be like at a high school level. All the questions were over the surface questions except a couple. I read through the questions first really fast, then scanned essay and knocked out question by question.
As for the percentile, all I think it means is compared to others who took the same test, that's your percentile. So my bio percentile is crap. I hope colleges don't see the percentile.