One of the most striking failings of Warhammer 40,000 ruleset is that the enemy is free to do whatever they want during their turn as there's no such thing as overwatch. It does exist in Victory & Valor, activating during the movement phase. There's also the defensive fire phase in the middle of the enemy turn as well, which allows units who didn't get to overwatch shoot as well. So you can't just easily go into the ideal position and fire at the enemy with impunity.
