Try giving your Armored Cars a retreat ability - so they can run when they’re under attack.
Cavalry Withdrawal: After one round of battle the Defender may withdraw one surviving Armored Car unit to any adjacent friendly territory. After the second round the Defender may withdraw a second Car unit to any adjacent territory (this can be a different territory from the first round). The Armored Car unit always gets its defensive shot in before it withdraws. If it withdraws it must do so before the Attacker starts the next round of battle.
I originally wrote up these rules for my variant rules for Classic A&A, available here.
-M_R