Length doesn't really say anything about scope. I can take MIT license, one of the smallest and most permissive license out there, and add a single word which would make it incompatible with every other license in the world including itself.
The only saving grace with FLOSS licenses is that they are not contracts, and only impacts those who seeks additional permission to distribute copies of a copyrighted word. If someone feel they don't understand the conditions which the license automatically grants permissions, they can always go directly to the author and ask them.