you aren’t countering fighters
you’re in a Buccaneer
I mean the PL-5B and PL-11 don’t have any special characteristics, iirc the PL-5B has a just barely smaller seeker FOV than the 9G (2.4 vs 2.5), and the PL-11 is a copy of the Aspide which is very similar to a sparrow, not to mention guided by a non-pd radar. What might be getting you is the PL-5B’s very high TWR, which means it can close the distance quickly and “ignore” your CMs by being too close by the time you start flaring. Aspides can be distracted by chaff, but like with all SARHs sometimes even though the radar locks the chaff, the missile still tracks you.