[Cross]

I would guess (because your unit is short of ammo) that they have been spotted by the enemy. Therefore the enemy is shooting at your guys. When a unit takes fire they will usually return fire regardless of the 'max range'.

Max range is more useful for unspotted units that want to ambush or wait until the enemy is closer before opening fire.

If you want to preserve ammo during your opponents turn. You could turn off some or all of your weapons, or perhaps just the longer range weapons. eg. Turn off the rifles but leave the SMG turned on.