say a mist guardian unleashed a rook blast, someone blocked it then that blast would be stopped in that direction, or someone used a cone attack if you blocked the attack then the space you are on would be safe and a cone of spaces behind it would (defenders block doesn't count as if there is a linear attack it doesn't flat out stop the attack from continuing on)
Interesting but is the purpose of such Magic attacks not that they go trough/to then around and past any target regardless id that target blocks for itself. Would make such attacks a lot weaker if there be safe zones behind a blocker. Think of enemies using this. A row of baddies would be impossible to damage with such a blast attack if the first enemy where allowed to block it for the rest.