<p>I might have advised phrasing a couple of things a little differently in the letter, but overall, a good idea, and a clear explanation of how someone with a near "perfect" academic record could end up being low in rank (not top 10%). Based on the fact that top schools tout that the vast majority of their accepted applicants rank in the top 10%, or in some cases top 5%, the OP has a legitimate concern about his/her ranking being perceived as "low."</p>