1. First off the two main powers of both their sharingan have many things in common. Both kakashi's and tobi's sharingan's alter dimensions kakashi can send objects through dimensions and tobi can send parts of his body through dimensions
2. In the recent manga as everyone knows kakashi tried to end the gedo mazo by sending it's neck to another dimension, however it did not work. This i believe was not because of the gedo mazo, but when kakashi tried to send it to another dimension, tobi simply brought it back with his own sharingan.
3. Something also intrigued me in the manga and I think it further supports my evidence. At the end there was a crack in tobi's mask and I think i know how it got there.
As you can see in the second row of panels, kakashi uses kamui to make the kunai disappear just as naruto's fist reaches tobi's face. The panel right next to that shows the kunai just about to disappear as naruto extends his chakra arm. This is when i believe naruto mad contact with tobi's mask. How did he make contact with his mask? Because tobi was unable to become tangible while kakashi's kamui was still open. Once the kunai disappeared tobi became untangible again and naruto was only able to make a crack. I believe this is because kamui and tobi's space-time justu are connected dimensions so they both cancel each other out.
This is just my opinion tell me what you think!