Neither of you have said what the rotor is hitting that causes the rotor not to seat on the hub.

If you can't see what's interfering with the rotor by looking at it from behind the hub, maybe you could place some modelling clay on obvious things like brackets, hub, wheel studs, suspension arms that it might be hitting.

Its not like the rotor's just floating there in thin air, refusing to mount onto the hub. Something is in the way. Find out what. Post.