User blog comment:Asfidyll/Valtor, Bloodknight of the Fallen/@comment-7709681-20140114032114/@comment-10253076-20140114042133

Plus, his ultimate specifically states "For % of his maximum health spent on this ability". The cost of the ability is 50% of his current health. If at full health, it means he used up 50% of his maximum health to afford the ability. This leads to 250 range and 150 AP for 8 seconds only.