I have never heard of the AFA stating this is the criteria for requirements regarding an LOA. In the end you just have to have a really strong resume in all of the WCS areas. The candidate that has a 2400, 4.0 uwgpa, may not get an LOA because they fall weak in the ECs or have a low CFA. While the candidate with a 2200 SAT, 3.7 uwgpa, Capt of the football team, maxed the CFA, President of the debate club, and Eagle Scout may be offered one.
The key is they are rare and in the end they do not mean a darn thing at I-Day.