differences are not small, Migs and Flankers don't share radars
two completely different radars of different class, from two different manufacturers (rivals at that time)
but they operate in similar frequencies - similar enough for highly sophisticated western RWRs like ALR-56 to not tell one from another
but third party developers think otherwise ... I remember Gazelle could tell a 33 from 27 even though they share same radar, lol
p.s.: Su-27, Su-27SM, Su-27SM3 (what's Su-27SM2 btw?) share same radar - N001, the latter flankers have a slightly updated version with A-G modes (N001VEP), but signal power, processor and antenna are still same