Raptor may be IR stealth but IR band is not the only one that EOS is looking for. There was a video on youtube discussing this issue.
And by the way, the moment Raptor turns his APG-77 on, it looses its main advantage, which suppose to be stealth.
Raptor is an excellent airplane. But, PAK FA is shaping to be a good match for it.
Reminder: SAM = Stealth STOP!