Hm, this is very opinionated, in my non-bias/logical-thinking, conciseness and formality is definitely a requirement in an adjustment letter. You do not have to be polite(courtesy), as long as you’re being direct and explaining yourself clearly. Sometimes being too nice can lead off into a bad end of the person you’re writing to thinking they’re right. Show the person who’s in control and explain to them in any way you can where they’re right and where they are wrong in the most rational way possible. Facts>Feelings.