Blocked Fire and elevation, 4th Ed.

[J6A]

BTW, the main reason I think I've done it as reciprocal is because the rules talk about the "If I can see you, you can see me" situation. I just extended that to "If I can shoot you, you can shoot me" or, in this case "If I can't shoot you, you can't shoot me." That doesn't mean it's correct, though.