Board Thread:Warhammer 40k Novels/@comment-27376167-20151210113237/@comment-24091837-20160415235158

That particular Primarch may perhaps have had mental abilities that bypass soul resonance & The Warp problem, and act like Telepathy does in other science fiction/fantasy tales, so that it is mental contact between the minds of two, or more organic beings. Thus being more akin to Psionics in D&D, than the traditional Psyker abilities of his Brothers' Legions utilise. It would most likely be a quirk unique to him & his Legion.