You do not need wrath of magnus to run this formation, it is in the crimson slaughter book only. Also it is any time you roll those two numbers, so each time you rapid-fire a bolter, take a leadership test, charge, you could trigger the summoning.
"That which we foolishly call truth is only a small island in a vast sea of the unknown. For man to truly flourish, he must be willing to abandon the ever-shrinking island of such petty 'truth' and surrender himself to the reality of that which is beyond."
Dark Apostle Erebus, architect of the Horus Heresy