Razor doesn't have a "filtering level" exactly - it just marks something as spam or not spam. The panel has an option (specifically indicated for POP3 users) to just tag suspected spam, rather than moving it to a different folder.
Overall, Razor isn't a very good filter. We implemented it a long time ago because it was easy, not too resource intensive, and better than nothing. As you may have noticed, we're working on some new options, which should be a lot more effective.