Tried both "0" and "3" values for "incap", played with the "order" setting, but the tank always attacks the incapacitated when their target is standing right on top of the him. Obviously he's not targeting the incapacitated survivor directly. If you run around while he casting attack animation, he will turn and look directly at you, but every punch he throws target the incapacitated survivor if they're nearby. Recorded a video:
https://www.youtube.com/watch?v=Je3PBHxzalg with l4d_target_override enabled