I see that alot of ppl have trouble with this part. I found its fairly easy if, when fighting the first group of enemies, allow one to live. Otherwise the rockets come out, and it sucks big time. With one still alive, you stay far enough so he shoots you. When he reloads, go into firs person and start tapping the screen to fire. If you keep doing it fast enough, when the guy shoots you, you wont flinch. It may hurt a bit, but if u have some healw and have on moon armlet/white helm then you should be fine. Well, I hope that helps.
"Guess i'll logout and check my email or somethin."