I don't play a mage much so made sure to test this before I spoke any further, but no you're misunderstanding.

If you and I are fighting, Monk v Blackmage and both locked on to each other, that allows me to easily circle strafe around you, but if you cast a spell at me, it will auto-face me, however, if i run around you while you're casting your character will not keep looking at me and if you finish the cast while i'm out of whatever conal range they have set, your casting will be interrupted.

If I'm not locked on you I can just run back and forth through you.