I have not seen any character limit in the "report comment field" and mostly my reports consist of a single word or two "Spam". The rest I leave on the moderator to judge the comment and delete it or leave it. It's tough though to write in a single line text box and I need to press the home and end buttons to re-read my reports.
IMHO you should add more details when reporting. For example, if you just add "wrong section" and if mods see any other reports about this topic, they will move to correct section. When they do, your report will go to another mod's queue. When he looks, he mostly likely will mark your report as "bad" as the thread is in correct section and mod won't know whether you made the report when it was in other section.
Borrowed from BadBear's post.
P.S. This wouldn't be a problem if you don't care accuracy rating.
BadBear's post is better than mine:
I don't know if I get you exactly. If it goes from hilariousandco's queue to mprep's, how could the report be handled? Can he know if the report was moved earlier or should he have to look modlog? If modlog is the choice, the limitation of the actions showing will affect, right?
Educated guess. If the report just says "wrong section", and at that point it's in the right section, it's probably going to be marked as a bad report. If it says "move to alt currencies", or "is not bitcoin discussion" then he'll probably know what happened and mark it as handled. It's not exactly an uncommon thing, and the mods are smart folks.
It's part of the reason why people shouldn't stress over percentage points.