School asked me to write an addendum for the LSAT

One of the schools I applied to requested that I write an addendum to explain my multiple LSAT scores (I took the LSAT 4 times over 2 years, went from a low 150 to mid 160). My score distribution across the four attempts shows a steady incline, the jumps from test to test are 4/5 points each.

Do I format it like a letter to the admissions committee? Should I just explain that I changed my study strategy and got more familiar with the test over the two years? Do I have to discuss why I wanted a higher score after the first attempt?