it's not only length that matters (no peanut gallery comments plz)..
but frequency.. the full text index won't the most common words.. or effectively those that appear with a relevancy of 50% (don't hold me to the number) or more..
ie: assume you had a forum about basket weaving... the possibility exists that the word 'basket' appears too often and therefore the index won't match on basket...
there is a lot more to it than just the simple example i give, but i wanted to bring that up
