User blog comment:Emptylord/Archived/Rasper the Frightful Ghost/@comment-4652200-20121017155042

On E:
 * Percentage: 8 / 11 / 14 / 17 / 20 % (+ 100% AP)

This means that you get 1% per 1AP e.g. if you have 60AP it will do 80% dmg at rank 5...

(+0.01% per ability power) is the "standard" for these types of scaling.