The Warden can't hit you with his shriek ability above 20 blocks

Put the summary of the bug you're having here

What I expected to happen was...:
I thought that the Warden would hit me with his shriek ability.

What actually happened was...:
The Warden just stayed in one place, thus allowing me to hurt him with my bow.

Steps to Reproduce:
1. Go to an ancient city
2. Summon the Warden
3. Pillar up 20 blocks