We don't have MAP but a test that sounds practically identical. I looked at the chart of norms, and reading scores are generally higher than math, but with different percentiles. I find the percentiles a lot more interesting than the actual scores. So my DD has alwsays had a higher reading score, but it was a lower percentile than math. DS showed this trend as well until the last test this fall (just a few days ago), his math was actually slightly higher than his reading score, which has never happened with DD. I think it's because he is so extremely high in math. I also noticed that for "most" kids, scores drop over the summer (quite significantly, like one whole grade level!) but this doesn't always happen for kids in the top quartile, esp. in reading. Kids in the top quartile are probably reading over the summer, and their scores keep rising.
