as far as I know, as quicklet pointed out, max up has an effect on this.
As I understand it, the amount of hate lost by a player due to damage taken is based on what % of their total hp that damage represents. For example a player with 100 total hp gets hit for 10 damage, that represents 10% of their hp and a large amount of hate lost compared to a player with 1000 hp, to whom 10 damage only represents 1% of their hp. I'd never seen evidence to dissuade this belief, and the idea carries with it the benefit that not only would hp gear serve a pld well in taking more/larger hits, but also to retain hate more easily. Even if it isn't true, I WANT to believe it haha.
Anecdotal evidence that reinforces my belief is often seeing, when a pld loses hate, the mob hit a blm once, really hard, then moving to the next one. Also, it would account for the increasing amount of hate higher level cures produce, not only because they cure more hp numerically, but because they represent a larger % of the targets max hp as well.
If this theory has been disproven, I'd like to hear about it, cause I try to be a knowledgeable pld if possible.
Edit: I thought that CHR thing had been disproven long ago. As far as I know, for tanking purposes, the effect of CHR is to increase activation of "killer" effects. I'd be interested to hear if it did more, but I don't think so.