Comprossion of the cord is called spinal cord compression. Compression of 30% of the canal can cause myelopathy but not always. I have seen myelopathy with only 10% cord compression and no myelopathy with 50% compression. Nonetheless,I would be concerned with a 30% canal compression for both myelopathy and the chance of a central cord injury.
See;
https://neckandback.com/conditions/cervical-central-stenosis-and-myelopathy/ and
https://neckandback.com/conditions/central-cord-syndrome-spinal-cord-injuries/
Dr. Corenman