1. It is not dangerous. The system is designed to allow for this.
2. It needs to be fixed. It will not be accurate nor consistent until you fix it. Eventually you will create wear between the index pin and the upper receiver slot as well.
It is common when a receiver just lines up at the minimum torque spec, that it will require a LOT more torque to get to the next gas tube alignment. 20lbs is BELOW the minimum torque spec. 70lbs??? That's nothing. The recommended spec is from 35 to 80 ft-lbs.
What you do - is back it off, and torque it to 80 lbs, and repeat, over and over, until 80 lbs will get you really close, then you just go until it lines up. Or, buy a different barrel nut, or get a receiver lapping tool and remove material from the face of the receiver, or use shims (shudder).
I just back them off and retorque to 80, and repeat, and this usually comes real close within 15 torques or so.