Generally speaking you shouldn't manually adjust ranking parameters unless there is a really clear case that applies as this may have a negative effect overall on your site - tuning is a better way of fixing ranking issues because it runs an optimisation process using training data that you provide to it.
If all of your URLs are long on the site, or the site is very flat then reducing the URL length factor to 0 won't have any real effect because every page ranks about the same on that factor (if that makes sense).