The Anti-Bio beam in FTL only damages crew, and - as with any beam weapon - it's often tricky to line up the perfect shot on an enemy ship. I understand (based on answers to this question - How do beam weapons damage enemy crew?) that a beam's path must specifically cross crewmembers - and not just the room they're in - in order to deal them damage.
Is it sufficient, however, for the beam to hit the square / tile containing the crewmember - or does the beam's path literally have to cross through the actual crewmember's sprite? That is, if a beam 'cuts the corner' of a square containing a stationary crew member, but doesn't actually touch the crew member, will they still take damage from the shot?