Diffraction cone of a ray which hits a vertex of a wall.

I have a problem visualizing the diffraction cone for rays coming from different sides. Although I've read multiple papers on the topic, my math skills aren't strong enough to fully grasp it, as I'm still an undergrad. I understand that diffracted rays start around the specular reflection and form a Keller's cone around the specular ray. Could you explain how it should look in 3D when the ray is coming from the side?