Sounds like you solved the mystery. My experience is when a pred is chasing your chickens they WILL wedge themselves in the tiniest places to try and hide. I came across a chicken death just outside their run (When I used to let them free range without me being outside with them) and one chicken lay headless outside with feathers all around. The other two made it back to the pen. One was inside the coop and the other (who I thought was dead) had wedged herself into the hollow part of a building block that was laying sideways under the coop. I had been outside for several minutes and there was no movement from the chicken stuck in the block. I figured I had lost both and reached down to pull the carcass out and when I slid her out she looked right up at me! She was playing possum! BTW, I pretty much determined from the dead chick that a hawk had gotten her. Head was gone and the neck was all pecked to the point of being featherless but the skin was otherwise intact except of course where the head used to be (crop and all other organs intact).