Sorry dude, you've skipped over the 'unmodified' in the spell description , the spell states the roll changes to an 'unmodified hit roll of 5+ instead of 6', or 4+ if charging spear armed dearthriders.
Would have been interesting but probably not intended. think i'll stick to swords over spears, with a liege kavalos helm of ordained and the command ability plus petrifex command ability they're looking quite nice.