There seems to be some kind of targeting problems with most spells. I'm guessing they target the center body mass or check ground level or something. Bows can hit those higher elevation targets, but you see a line from yourself to the target, and can target any visible part of the enemy. Spells don't have a targeting line like that, except things like magic missile or scorching ray (which in my experience successfully hit anything that a bow can hit).
That would explain it. I'd consider it a bug, but this is a reasonable explanation. Thanks.
