So you're saying a shinra tensei took away 120% of his chakra? Because that's how much extra chakra he would need to use kamui 5 times after everything he used against obito.Kakashis chakra usage with Kamui depends on the size of the object. After getting his chakra restored Kakashi fell to ground right after transporting the Hachibi. So there is no way to tell how much chakra he actually uses, all your dumb math goes right out the window.
He received a shinra Tensei to the frikking face, the damage of that alone would affect his chakra, and he still used it twice before dying.