They've always seemed quite aggressive to me (
see here)
I always see them chasing friendlies. I get quite a lot of kills by picking them off the six of other P-51's etc.
I think they perhaps toned it down a bit though, as there are generally quite a few enemy fighters and I'm not that good; I should be shot to pieces! Their gunnery skills are rubbish!
And my wingman is very observant - he ALWAYS tells me if there's one on my six! Damn good eyesight that boy... lol