Some example videos of heat seeking missiles and how they acquire their targets:
This is what it should be like: http://youtu.be/Tl0mAWYNaw8?t=39s
Or to make it easier on the developers, even just this: http://youtu.be/RWdIm5Q6t28?t=1m36s
Read the parent thread of this ticket here: http://forums.bistudio.com/showthread.php?180867-Air-to-Air-missiles-and-why-they-need-to-change