Game Mechanics: Range not being calculated properly on Z axis

[Mouse]

Its easiest to tell when fighting in a hilly area against specs. If on a plane, when they come into range of Lightning strike, you can cast your spell and move away before they do their lifetap. If they however are coming down a hill at you, sometimes they get close enough to lifetap you before your cast is even done because the distance is so screwy at angles.