Chance to Absorb is 5% per 1000 Max MP. MP drained is 5% of your max MP upon taking any form of damage including damage from spikes. Taking 0 damage from stoneskin also drains your MP as well so be cautious if you utilize this.
If the chance is 1% per 5% consumed then this should be 100% for a char with 2000+ MP. Consuming 100 MP per "Dmg. Taken." This is dependent on the above assumption, that this is a whole percent and that the mana usage isn't based on "current" rather than Max.
