Loic, from my experience, he'll only engage between about 175 to 300 metres. Don't know why, but if you fly into the middle of a formation - try Dakotas, as they don't shoot back! - he'll get overwhelmed. Like a lion with a herd of wildebeest! No idea which one to attack, so he does nothing. If you stay outside the formation, once he starts shooting - rarely where you want him to - he'll get on with it.