Book chapter co-author should be indicated. Try not to mention the award is only for "students". Use scientist or reseacher instead of student when possible. In your reference letters, there should be a couple of indicating "I have never worked with or supervised or talked with Dr.xxx. I know Dr. xxx through his publications and reports or reviews by independent scientists, blah, blah...". I guess INS is raising the wording criteria for EB1a as the case volume increases. Although I don't see any problem with your background,I recommend you spend some time to edit or re-organize your documents unless you think nowhere can be improved. Good luck!