Playing the game I like to see the numbers and see the numbers make sense...
One shouuld count both sides the same. Either the count is 3 vs. 5, or the count is 7 vs. 17.
The counts really shouldn't be mixed as it is right now. My suggestions if you do use the 7 vs. 17 method, then the tool tip from each of the highlighted units should include a unit count within the group. (Case 2:)
Case 1: Battle change reflects the stack count: I can see that it is 3 stacks vs. 5 stacks, and if I highlight the first mite I would see that the unit count has 4 creatures.
Case 2: Battle change reflects the actual unit count: I can see that it is 7 units vs. 17 units, and if I highlight the first mite stack, I would see that the unit count has 4 creatures.
Case 3: Battle changes reflect a mixed count: I can see that it is 7 units vs. 5 stacks, and if I highlight the first mite stack, I would see that the unit count has 4 creatures.
Case 4: Battle changes reflect a mixed count: I can see that it is 7 units vs. 5 stacks, and no tool tip changes. (a.k.a. leave it alone)
Note: I can already see that it is a 3 stack vs. 5 stack. The UI is not telling me anything that I visually cannot see myself.