F15 had similar RCS, Yet no one caught that rhino. Son , the RCS doen't play any role in 4th Gen fighters. I suggest u to learn some thing about detection and tracking range of fighters. Even one detect any plane on its radar, it's not sure that it can track that plane for long.
No matter how less you keep the RCS, for 4th gen fighter it won't be lesser than 5m2 , in loaded configuration. And mind that this is just frontal RCS, assuming that the fighters are approaching each other at same altitude.
Even F16 detect Su27 family at 200Km, so what?? Can it successfully track it?? Does F16 has 200Km range AAMs??? As I know 100 KMs is max AAMs range (some say 129-130, in approaching mode, 50-60 in chasing mode). To lock Su27 or F15 one need to come within locking range (80-100 KMs). In 80-100 Kms (BVR scenario), only thing matter is Counter measures, evasive manuver , ECM suit etc...
Here Big Fighters have advantage, Due to huge size they have enough space.
In BVR scenario, if both fighters belong to same generation, same class, 1 or 2 BVR missile can not guarantee the Kill..