True tanks don’t protect infantry. However, planes and bombers and tanks don’t target infantry, unless that’s the only remaining targets. So you should be allowed to sometimes pick which units are removed. I think a rule stating that if a roll produces a hit number and there is also a 6 rolled then the roller gets to pick which unit is removed for every 6 rolled.
Example: rolling for 4 tanks, 3,2,5,6 get rolled; so there are two kills and with the 6 being rolled that means the roller gets to pick 1 unit to kill.
This would help establish the reality that the attacker would be targeting higher priority targets while also maintaining the reality that those attacks sometimes miss and infantry are the casualties.