For the question that the tension screw doesn't work and can not lock the tilt mechanism, My lens keeps moving down on the tilt.

The solution is there is another small screw beside the brass tension screw, You have to tighten this screw with screwdriver.

This will help you the lock the tilt portion of the adapter better, so the lens will not slip down on its own. 

There is a double locking mechanism on the adapter. But if this screw is too tight, it may cause the movement of the tilt mechanism not to be smooth or can prevent it from moving at all.