Malachai, as mentioned in the background thread, is a hardliner Cult Mechanicus, even by Tech-Priest standards. So Tia being a filthy xenos isn't nearly as big of a deal as her being a xenos who uses all sorts of strange alien technology and keeps<em>thinking machines</em>as<em>pets</em>, and accounts for her getting a 'warmer' reception than anyone else - but he still effectively rules the Enginarium as his private domain within the ship, only leaving for away missions or emergencies. The Astropath is the only person he won't aggressively chase out if he finds them trying to get in.<br/><br/><br/>EDIT: Oh, and with his new Hulking mutation, he's a little over 8 feet tall. Corridors are not a fun experience for him, so he doesn't get out in person much. But on the bright side, if you need someone to take a multi-melta blast to the head and walk away, he's there for you.