The whole line of lull spells is pretty horrible without very high charisma. If you have the kind of charisma that a paladin is likely to have in normal gear, it's rarely safe to cast it at all because there's like a 30% chance to just aggro the whole batch. You really need 150-200+ charisma to comfortably use lulls in any setting where a hard fail is dangerous. It's pretty much just an enchanter thing. And of course Harmony for druid/ranger since it's unresistable.
I'm quite sure charisma affects not only the chance of crit resist but also regular resist. That is at least the case with the undead lulls. I just leveled from 26 to 31 on that one 4-spawn skeleton house in LoIO over the last few days and it was very clear that the lull got resisted way more than normal spells, presumably due to my iksar's 50 charisma. Low blues that would resist snare no more than 5% of the time tops would resist lull easily 30% of the time.
The rank of the spell doesn't affect resist chance unless the specific spell has a negative resist modifier, which I don't think any lulls do in this timeline except for Harmony. The ranks affect what level of mobs can be targeted and how much their aggro radius is reduced. With the low-level versions, mobs have to stand a fair distance away in order to not add. With the high-level ones they'd have to be french-kissing the target to get pulled along.
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