What determines the odds window's presence or absence?

[Hierophant]

I have to wonder sometimes, what dictates whether the odds window shows up before a battle? When I use anti-air units, sometimes the odds window just doesn't show up, and that usually means I'm going to lose immediately. It's very frustrating, especially when it should be an easy win (fighter plane with superior weapon v bomber plane with no armor sort of thing). Why does that happen?

[bvanevery]

I haven't had enough air combat lately to be sure of that case.  I'm pretty sure that artillery duels don't get the odds window love.  You just go straight to shooting at each other.

[Hierophant]

Talking about air battles specifically, it seems to happen mostly on the first times I use fighters. And it always means I'm going to lose the unit I'm attacking with. But after a while, it stops happening.