At the lower left hand corner of the last page, state in a short sentence the history of the association. Remainder of body text - should include an relevant information. Brief history of the organization - one or two sentences. The longer letters are also more likely to be edited. It's better that you do your own editing.
Most people read the shorter letters first and then perhaps later read the longer ones.
Thus your shorter letter has a better chance of being read. State the argument you're responding to, as briefly as possible, in the letter's introduction. Pick an issue of particular importance to you - don't be afraid to let some passion show through. Stick to a single subject. Deal with one issue per letter.