There is
first question is are you asking about the original version or the new 1.5 version of cow that is available in select games?
In 1.0 version there is an effective number of each unit type, and after that additional units are just along for the ride. For example a group could have 8 infantry, 8 anti tanks, 8 anti air, and 6 light tanks. All 30 units would be 100% effective in combat. This is called the State Based Damage Efficiency, and there is a list of the optimum SBDE numbers pinned here in the forum.
in 1.5 the limitation is stack based instead of unit based. This means that only the 10 strongest units in the group
Will be used in combat, and the rest will be simply along for the ride. If using the same stack as above consisting of 30 units there will only be 10 used in the combat calculation. This will be the 10 most effective against the chosen target.
