Actually that was kind of a false alarm. I didn't take into account rounding error and got my modifier wrong

. The CE loss actually seems based on either only Max HP or a combination of player level and Max HP. So far, it seems like the higher your max HP, the less hate you shed per 1 damage taken.
I'll have to get more real values to see how this scales with your max HP (especially at level 75), but it does seem to vary quite drastically since at 75, max HP totals also vary quite a lot. This may be a convenient explanation as to why a tank can take quite a bit of damage without losing hate while a mage can take 1 shot and lose hate quite easily.
Enmity gear either way doesn't seem to affect this but I'll have to formally debunk it later. I'm almost positive Foe Sirvente would affect this just because I can't think of anything else it would do and it fits the description quite nicely, but I haven't actually tested.