I think it’s by design, otherwise there’s clipping with hair. With the hood, there are also pipes on the back, so likely something hidden - like a contact plate.
Those that have hair noticeably clip:
Obscurus Mk If Psykana Collar - hair clips while running and head tilted:
Edit (11/12/22): Moved clothes / garment clipping section to:
Psyker clothes clipping - Warhammer 40,000: Darktide / Bugs - Fatshark Forums (fatsharkgames.com)