Fluff-wise, Block It ALL With Your Chest would make sense for it to only block the area behind the Muscle Man (making it dependant on your location how many people would be safe from it), but you could add in a Tumble check DC 15 + amount of feet, to which you recieve your Strength modifier, that you may use as an immediate action to move yourself into the way of the AoE to block more of it.

Instantly also adds a movement aspect to the class.