[NickMPK]

I used to intern for a US Senator, and when we would get letters or phone calls on a specific issue, we would keep a tally count in support and opposition. We would also send out response letters, but for each issue there was basically a form letter sent to supporters and one sent to opponents.

So basically, it doesn't matter how long the letter is as long as you make it clear what side you are on. The congressman will almost certainly only see how many letters he got on each side of an issue, and not the individual letters.