Good idea, but a bit late? Removing the foundations allowed him to spawn and I got a bit stuck while climbing down (no hearts of the hero with me) but with my arrows from above and two on the ground we only had one death. After a bit of climbing practice in solo, I can get him alone without much problem, or be prepared with the hearts.
The only thrall we had remained passive and was of no help at all. Mine decided to remain on the perch and didn’t help at all which was odd because she originally ported to the ground, then back up to me.
All in all, a success, and due to your spawn blocking suggestion. Although, I thought the land claim to be limited horizontally, but not vertically, which would not have done the trick. I may test that lowering of the radius and see what happens.
Thanks, and regards