If someone wants to finish off a dying enemy plane I popped, let'em. I've got enough kills already. I'm just concerned about keeping the barbarians from getting to my homeland.
I'll push an HO merge if I think I can win it. Curiously, most of the HO's I see coming at me are in Spitfires, LA7s, and N1K2s. My eight .50cals, or four 20mm, or single 30mm with twin 20mm gun pods are usually sufficient to deal with these types of attacks. I'll dodge the ones I think I'll lose, such as when I'm in an FM2, P-51B, or Yak9U.
I'll engage a higher enemy plane if I get bored with charging into hordes of barbarians doing their P-51D and Typhoon base porkage runs.
One thing I've noticed about the BigIsles map is the dependence on carriers for base capture. The actual capture might come from a C47, but the fighter suppression usually has a carrier involved.