There are a lot of enemies and weapons where getting headshots feels wonky. In particular, any attack that needs to be aimed slightly upwards (against CWs, this is practically everything but clean overheads) easily hits the body even when aim is in the middle of the face, and Halberd at least seems to take the hit target from the blade rather than the spearpoint, even on thrusts. I think the first part is because teh head hitbox sits immediately on top the body, with their edges aligning or the body being a bit more forward, so when a hit comes from below, it often hits the chest first, even when aimed at the head. Aiming above the head does help with this, which seems to support that theory.
All the Lords are pretty tall, so this certainly applies, but it is also possible that their weak points are somewhat smaller than usual, which would worsen the issue.
Also try headshotting the training dummies in melee for some fun wonkiness (well, really to see this issue at work).