@Setec Astronomy Thanks for your reply! Yes, the results were as you have described.
The car hasn't been clayed for the last 3 years and it's a rather neglected car, although surprisingly it didn't had a bad buildup of contaminants as per touch/bag test. Of course, you could have just a 2nd application with FerreX, however I'm just striving the efficiency that is possible. This method was presented by Yvan Lacroix and is used in his shops. I really respect Yvan and trust his knowledge, so I'm assuming that this method is working or at least working to an extent that is necessary. This is the point here that I'm not sure about, did the method worked as expected and there is no need to strive for "perfection" by removing "all" iron contaminants or there is just something to tweak on the process?