Specifically the dorsal and anal fins should not greatly exceed the body width
and the caudal fin should not exceed 1/3 of the body length.
It is found at the very top under Plakat Standards. When reading further down under Show Plakat everything stays the same except just a few things not having to do with the anal or dorsal size.
If you aren't interested in traditional plakats it's easy to miss. That's kinda the way the standards are set up though, you have to read the whole thing to see what standard stays the same and what changes between variations.
I am looking at 2010 standards. I went to the IBC website to find the newest standards and I do not see them or a link to them. What's up with that? I know I downloaded them last year when I joined but that was the old website.