[@Bloodrose] More or less, yes. Have you read "Fulgrim", by chance? It has a good example of what I'm trying to describe. In it the Emperor's Children long before the official start of the Horus Heresy are fighting some psykers, and one of the Emperor's Children is being simultaneously held in place and mind being burned away at by one of the enemy psykers. Whereas some other Marines were powerless to such treatment the guy in question did a grand scream that was enough to daze the psyker for a few moments, enough for the playing field to be levelled so the Marine could go shoot and stab the fellow as Marines do.