Good question. But you could just test it (make a mystic with lv 11 absorb soul and another one with lv 10). Even if this is true, lv 11 absorb soul has to somehow hit harder, because then what would be the point in making another version of it?
The thing is on PWI Mystics said level 10 absorb soul hit a lot harder as it doesn`t care about the defence levels.The lvl 11 only gains additional chi but hits a lot lower on high defence levels.Somehow this lvl 11 absorb soul was a "fix" with the defence level system.
I want to know if level 10 absorb soul hits harder but it takes time till I get another mystic to 150 with same gear.
On topic: Lol pwi mystics...funny, lvl 11 absorb takes into account your matk and current atk lvl, yes. But it deals based on that vs the target's pdef. In other words, defense level, physical immunities and reduce physical damage on gear has no effect on Absorb Soul's damage. It however, deals status damage, so casting faith will cancel AS's damage completely