So was trying out Corsix's 100 absorb against Khors smacking. It did seem that the cost did not depend on damage at all, as some attacks were stopped for as little as 1sp. The other problem is that this is random, i know the 'chance' to absorb is based on stats/the skill but this random element is kind of bad. Khor could 20-50 damage Corsix (with adrenalin hellfire sagaris and corsix using shield spell)
So i 'could' kill Corsix in 3 hits, or i 'could' kill him in 60.
Should cut the RNG, abosrb works on every hit until you run out of SP. Increase SP cost to scale with damage, maybe at a rate of 1sp per 5 damage eaten regardless of how much health you gain for this. That would make it literally as SP efficient as the Heal spell. On second thought, thats 500 damage absorbed for 100sp (still less efficient than it currently is in pvp!) So 1sp per 5 health gained tacked on. (at 200) So it'll absorb/heal hundreds on a full bar.
Since thats way more than a Wizard can deal before running dry, Absorb could be bypassed by spells (makes Lifetap sound good!)
For Corsix, if he wanted to use absorb he'd have to stick to Mana only spells for the offensive, SP is his mana shield and he wont be killed in 2-3 lucky blows. This applies to rogues too.