That makes sense for vehicles but I can see it being very painful to watch infantry that come under fire not run to a nearby building or stand of trees, etc. It's not something that you can pre-plan, and manually telling infantry squads to do this isn't the right approach.
Perhaps you can make an exception for infantry under fire, and have their formations automatically set to "free" when it triggers?
Perhaps it can be made a SOP option (subject to the command delay) after the release. However, it's not always that obvious if the infantry unit should start moving under fire or not. The player may have intentionally placed the unit to the location, for example to ambush the enemy, and if he forgets to set the option correctly then there may be unwanted results. It can take forever for a squad to advance 60 meters (two map cells) under fire, and while they move they have higher chances to get killed.
The more there are micromanagement options the more the human player can have advantages over the AI opponent.
Just bringing up some aspects that must be considered. What we currently have is that when the situation is very tough, or the morale level is low, the infantry unit retreats and may pop smoke if there are enemies in sight. I think Steel Panthers had it like this.