Maybe I have an idea.
You said that you are attacking a territories defended by 100 infantries with a defensive punch of 200, that are about 33 hits for the attacker.
When your forces of infantries and artilleries loses 33 units you are losing 66 in terms of attack punch.
With your forces of infantries and tanks losing 33 units means losing only 33 in terms of attack punch.
So in the second round first formation (infantries and artilleries, F1) have a punch of 134 while the second formation (infantries and tanks, F2) have a punch of 167.
So first formation losses in attack strenght respect to the second is double.
In the second round formation F1 will inflict 22 hits on the defender while the formation F2 will inflict 27-28 hits to the defender.
The defender will inflict 22 hits.
So in round three the situation is:
F1 45 art vs 45 inf
F2 45 tank vs 40 inf
I think that formation F2 has a greater chance to win the battle.
yes thats right there only equal in teh first round of combat. ayou have to recalculate after each round.