This could be a solution too. But it's an online game so 4 vs 4 it's more enjoyable, at least for me.
I dont worry about 1+3. If you have a party already it makes no difference between 4 vs 1+3 or 4 vs 4. And I really believe the most 1+3 are noobs farmers and with low skills in real fights. Without Lt. Major, Guard, Lt. Colonel, Colonel, etc SPY characters it will be harder for them to get high streak.
No i mean
If you go to the display where you see cities , troops and morale , you need to choose one of the battle that has 2 generals in it .
For example .
Jiang Wei - Cao Pi
If we just had one battle with 2 generals in it instead of 5 battles with 2 generals in it ,
It would lower the chance from alt farming and 1+3.