Good grief eskimo2, what did ya teach, underwater basket weaving?
Let me make this simple for you.
Historical CT matchup example:
Axis: 109G2, 109G6, 109G10, 190A5, 190A8.
Allied: SpitV, SpitIX, P38, P51B, P51D.
Regardless of your chosen side, your opponents will always be in the same 5 aircraft. 25 matchup possibilities.
Area arena matchup example:
Axis: 109E, A6M2, C202.
Allied: SpitV, P40, F4U-1a.
Since you can fly any aircraft in the set, you may be fighting against any aircraft in said set. Even with just 3 per side, there are 36 possible matchups.
Note: Not responsible for mathematical errors. Mathman wouldn't help me.