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I don\'t think the INS really cares about the difference between organic and medicinal chemistry (there is not much in fact), unless they ask about it directly in the RFE. They want to read words (not implications!) that you are the best thing after sliced bread, as someone said at this forum.

)) I beleive they just want more info that you are "extraordinary", "outstanding", "one of the top 3-5% in your field", "have sustained international acclaim" etc.
2-3 letters from people who DID NOT work with you directly containing such wording will help. To show international acclaim, get letters from different countries. As some people advised at this forum, don\'t be shy to ask people who cited your articles, or at least those whom you cited. Some of them will refuse while others will write letters for you. They also feel themselves more significant when they are asked to write expert letters. Also you can reemphasize and re-cite the most favorable words from already submitted documents.
You can also get a letter from Humboldt Foundation, or simply statistical info about how many applicants were competing for the fellowship, and how many of them were awarded. The numbers will be really impressive! Point out, it is a very prestigious INTERNATIONAL award, provide requirements for the applicants, let someone to state this fact in a support letter. Go to their web page (I know for sure, there is a link from
www.DAAD.de) Or try to get their annual report (it was easy to get a similar one from DAAD from their US reps). I am sure the INS clerks have no idea what Humboldt fellowship is. So explain them in plain English and simple numbers.
Good luck, you should be all right with your background.