Heat Seekers, IRMs are affected by two things, flares and heat blur (ground clutter, sun) in game that means, IRMs with low jam resistance may fail at low altitude and can lock on the sun itself. Early IRMs (low track rate and turn G) can be outmaneuvered, if you react quickly. Late IRMs can only be stopped by flares (a lot of). BTW each plane has a IR signature value like RCS but it is not set in any data ini, maybe in stealth only.
SAHM missiles are more easier to get rid of, at least they are prone to more failures. First, the search radar range is reduced by noise jamming. Second, the radar lock range is reduced by deceptive jamming. The guidance radar, IF not CW (countinous wave, or monopulse) RadarGuidanceCW=FALSE then also affected by deceptive jamming. If it is CW, then only CanJamCW jammers can defend against such guidances.
Third, the target has to be in the radar cone of the launching plane. Lock breaks, missile goes ballistic.
Fourth, such missiles are also affected by ground clutter, low jamresistance values mean very poor performance at low range.
Fifth, radar homing missiles are far less maneuverable than the IRMs, so if you spot them, or just start maneuvering, you have good chance to avoid them.
Too bad we have no usable eastern RWR set in cockpits, but I trust the cockpit GURUs will invent something )))
Most planes are being reworked on the eastern side too, so a lot more planes will have CM ejectors and jammers which they had them historically.
Also there is a serious bug in the latest SF2 version that AI planes cannot use external CM pods, a serious cutback to early MIGs. That means a Jul 2013 level patch will be released to provide a workaround (giving planes CM by default, internally)