[Support request] Root bound – can I do better?

I recently finished my first full auto-pot grow in coco with and overall very pleased with the growth and yield. After harvest I carefully studied the root zone during the breakdown and cleanup. The bottom of the 3 gal pot was total root-bound-town but every root looked healthy and white thanks largely to the genius of the air dome.

The bottom 2-3 inches of the medium and the entire air dome was a solid mass of roots but the 10 inches of medium above the dome had far less root density. I estimated 20% of the root mass was in the top 2/3rds and 80% in the bottom 1/3.

What can I do to encourage roots to grow more evenly through all the available medium?