Damage Reduction for absorption runes.

I was wondering how much damage reduction a minor a major and a superior rune give.

I was under the impression that it was like this...
Minor -1 damage taken
Major -3 damage taken
Superior -5 damage taken

...but im not quite sure so could somebody post back and clear this up for me.Thx.

I'm fairly sure that the progression goes -1, -2, -3, although I could be mistaken.

I think it averages out to be about -1, -2, and -3, but as far as i can tell, it is more like a percentage or something (i think i get more than -3 from high damage spells when compairing damage taken with my friend in the same armor)