Is the placing of covering fire templates restricted by the colossal's facing ?
Here's the rule as written on stormwall's card.
Covering Fire - Instead of making attacks with this weapon during this model's activation, place a 3" AOE anywhere completely within this weapon's RNG. The center point of the AOE must be in this model's LoS, ignoring intervening models. This model can not an place AOE for this weapon while it is crippled. A model entering or ending.. etc etc.
As my understanding, the 2 underlines are restriction for placing. RNG in all caps is a distance measurement, and the model's LoS is not split between left and right. So since it's not making an attack, I think stormwall can place its AOEs both in left field of fire or both in right field of fire. Want to confirm.